Climategate Revisited: New Theory Explains The Tree Ring Controversy

The tree-ring divergence problem, at the center of 2009’s “Climategate,” can be explained by normal changes in light intensity Mark Ralston/AFP/Getty
 




by Elijah Wolfson, Newsweek, May 7, 2014

In November 2009, climate skeptics had their day in the sun when an anonymous hacker posted years' worth of emails sent back and forth between some of the world’s most prominent climate scientists, working with the Climate Research Unit (CRU). Buried within these thousands of emails were a handful of fragments that skeptic seized on as proof positive that climate scientists had fabricated the idea of man-made global warming. After the emails were made public, a media frenzy ensued; “Climategate” culminated in deep investigations into the legitimacy of the science that backed of the theory of a man-made global warming. Ultimately, the CRU scientists were acquitted of any malfeasance, and their science was verified to be clean, but the events had a significant impact on public perception.

Five years later, a new study published in Nature Communications may help cool the lingering fallout from Climategate. The study, led by Alexander Stine of San Francisco State University and Peter Huybers at Harvard University provides a compelling scientific explanation for the issue at the center of the 2009 controversy: the tree-ring divergence problem.

Scientists are nearly 100% sure of the world’s daily temperatures for the last 150 years or so—which is when we started to keep daily weather records. But before that, it’s a little less clear. So many climate scientists, on both sides of the debate, have come to use tree rings, in conjunction with other proxy measurement tools like coral growth, isotope variation in ice cores, ocean and lake sediment records, and more, in order to reconstruct temperatures changes over years.

“The tree-ring records are in many ways the best record we have,” says Stine. “There are trees all over the Earth, and they have this annual resolution, which very few of our proxies do.” Trees reflect a more human time scale; ice core records show temperature changes across time periods on the order of millions and millions of years, while trees rings track changes year by year. In temperate climates (like much of the U.S.), trees only grow during the part of the year referred to simply as the growing season. In the Northern Hemisphere, this is the spring and summer. In a good growing season—where there’s plenty of precipitation and warm temperatures for months on end—the resulting growth ring will be relatively wide. In poor growing seasons, the rings will be narrow.

It’s not perfect, but it’s a pretty decent proxy for those years before thermometers and recordkeeping.

The problem, though, is that since the 1960s, Arctic tree-ring growth seems to not match the actual temperature records we have. Thermometer measurements show a sharp jump in temperature in the late 20th century. This is one of the primary arguments for man-made climate change: as the global population increased, and we began to build bigger and more industrial cities, and rely more on fossil-fuel based travel in cars and planes, humans greatly sped up the warming of the planet. But Arctic tree-ring records don’t back this up. In fact, they seem to indicate a decline in temperatures during those years. This is called the tree-ring divergence problem, and has been recognized, accounted for, and written on extensively—not the least notably by Keith Briffa, one of the CRU scientists singled out as supposedly burying data after the emails were leaked, in a paper published almost a decade before Climategate.

Briffa had put forth—and the scientific community had long-since accepted—the notion that this “divergence issue” was actually a strong decline in tree sensitivity to temperatures after 1960—and not the temperature themselves. In fact, Stine says, if you look more closely at the numbers you can see that year to year, the rings on an individual tree in the Arctic Circle still do change size with year to year temperature changes—there is just a “systematic underprediction by the tree rings” that began in the mid-20th century. “And when you average all the trees, everything goes away except for that systematic underprediction.”

In 2009, critics from latched on to one email in which Phil Jones, at the time the head of the CRU, wrote that in a recent graph (prepared for a World Meteorological Organization Report) he used “Mike's Nature trick of adding in the real temps to each series for the last 20 years (i.e., from 1981 onwards) and from 1961 for Keith's to hide the decline.”

It was unfortunate phrasing. Jones was referring to the famous “hockey stick” graph used by Michael Mann, the director the Earth System Science Center at Pennsylvania State University, in an article published in the journal Nature, in which he combined a number of different data sources to show overall global temperature increase over the years. According to Mann, the criticism was simply a “cynical misrepresentation” of Jones’s email, which he tells Newsweek “spoke of something that was already well known to the scientific community—that tree-ring density data should not be used to depict temperatures after 1960.” Following the release of these emails, Mann was extensively investigated for any scientific misconduct—and completely acquitted.

Today, Mann says that the whole Climategate fiasco was based around the misconception that the only evidence there is for climate change from the paleoclimate record (i.e., the record of the climate change throughout the entire history of earth) was from tree rings. “Nothing could be further from the truth,” he says. “[There are] multiple independent lines of evidence for human-caused climate change. And the most important evidence for modern warming comes from instrumental measurements—thermometers—not paleoclimate data.”

Stine points out that in most of the scientific papers at the time, researchers would typically plot tree-ring records and thermometer records next to each other—then make an argument about the gaps between the two. “I don’t think you need to argue too hard to convince me that thermometers are better than tree-ring records,” says Stine. “What got turned into a big hoopla was the putting together of a summary graph, to say ‘this is our best interpretation of what the numbers have been.’ ”

Nevertheless, Stine and Huybers set out to explain the tree-ring divergence data—mostly, Stine says, because he wanted to get a better sense of what the Earth’s most ancient trees are actually able to tell us. Their solution is simple, elegant, and intuitive: global dimming. Since the 1960s—exactly when tree-ring data started to go awry—“there’s been large scale decreases in the amount of light that’s reaching the earth,” says Stine. It’s fairly easy to see why, too. In rapidly industrializing parts of the world with fewer emissions laws—like Southeast Asia—the light decline is particularly steep, and continues into the 21st century. On the other hand, in areas like the U.S. and Europe, you see a rapid decline in the middle of the 20th century, but then light levels steady themselves later on—right around the time most air pollution laws were put into place.

Trees of course, need light to grow—they use photosynthesis to turn light energy into chemical energy to fuel all their activities, including their growth. “My hypothesis,” says Stine, “is that the light is directly affecting tree growth: You turn down the lights, you turn down tree growth.

In the scientific community, skeptics of human-induced climate change have mostly been silenced; the 2014 National Climate Assessment published Tuesday unequivocally laid global warming and its resulting environmental impacts at the feet of human civilization, stating ominously that “climate change, once considered an issue for a distant future, has moved firmly into the present.”

 

http://www.newsweek.com/climategate-revisited-new-theory-explains-tree-ring-controversy-250208

David Spratt: Is climate change already dangerous? Part III. Consequences from current greenhouse gas levels

by David Spratt, Climate Code Red, September 22, 2013

Third in a series

Danger from implied temperature increase

The current level of atmospheric CO2 only is sufficient to increase the global temperature at equilibrium by +1.5 °C, based on the standard assumption of near-term climate sensitivity of 3 °C for doubled CO2.

If all current greenhouse gases are taken into account, then: 

The observed increase in the concentration of greenhouse gases (GHGs) since the pre-industrial era has most likely committed the world to a warming of 2.4 °C (within a range of +1.4 °C to +4.3 °C) above the pre-industrial surface temperatures (Ramanthan and Feng).

And the 2007 IPCC Synthesis report (Table 5.1 on emission scenarios) also shows that for levels of greenhouse gases that have already been achieved (CO2 in the range of 350–400 ppm, CO2e in the range 445–490 ppm) and peaking by 2015, the likely temperature rise is in the range of 2–2.4 °C. 

These scenarios include short-lived gases such as methane, which degrades out of the atmosphere in a decade, and also nitrous oxide, which has an atmospheric lifetime of around a century. On the other hand, the fact that temperatures are not already much higher than they are today is due principally to the large-scale emission of very short-lived (10 days) aerosols, such as soot and exhaust from burning fossil fuels, industrial pollution, and dust storms, which are providing temporary cooling. The effect is known popularly as “global dimming,” because the overall aerosol impact is to reduce, or dim, the sun’s radiation, thus masking some of the heating effect of greenhouse gases. The aerosol impact is not precisely known, but Ramanthan and Feng estimate it as high as ~1 °C. As the world moves to low-emission technologies, most of the aerosols and their temporary cooling will be lost. Recent research finds that quickly eliminating all greenhouse gas emissions (and necessarily the associated aerosols) would produce warming of between 0.25 and 0.5 °C over the decade immediately following (Matthews and Zickfield; Hansen, Sato et al.).

A practical consideration of “dangerous” can include the question as to whether there are tipping points or “concerns” activated for the elevated temperatures that we are generally considered to be already committed to: conservatively in the range say +1.5 to 2 °C and, more pragmatically, in the range of 2 to 2.4 °C if all current greenhouse gases are considered. A related question is whether the +1.5 °C goal advocated by the small island states and surveyed recently by Climate Action Network Europe and Climate Analytics would avoid “dangerous” climate change and significant tipping points.

This is a broad topic, but four recent important research findings on impacts for the current committed warming are arresting:

Greenland Ice Sheet tipping point

The tipping point for GIS has been revised down by Robinson, Calov et al. to +1.6 ºC (uncertainty range of +0.8 to +3.2 ºC) above pre-industrial, just as regional temperatures are increasing at three-to-four times faster than the global average, and the increased heat trapped in the Arctic due to the loss of reflective sea ice ensures an acceleration in the Greenland melt rate.  If the lower Greenland boundary in the uncertainty range turned out to be right, then with current warming of +0.8 ºC over pre-industrial we have already reached Greenland’s tipping point.  And, with temperature rises in the pipeline, the upward trajectory of annual greenhouse gas emissions, the projected future increases in fossil fuel use, and the continuing political impasse in international climate negotiations, we are very likely to hit the best estimate of +1.6 ºC within a decade or two at most.

Coral reefs

Frieler, Meinshausen et al. show that “preserving more than 10 per cent of coral reefs worldwide would require limiting warming to below +1.5 °C (atmosphere–ocean general circulation models (AOGCMs) range: 1.3–1.8 °C) relative to pre-industrial levels”.  Obviously at less than 10 per cent, the reefs would be remnant, and reef systems as we know them today would be a historical footnote.  Already, the data suggests that the global area of reef systems has already been reduced by half. A sober discussion of coral reef prospects can be found in Roger Bradbury’s “A World Without Coral Reefs” and Gary Pearce’s “Zombie reefs as a harbinger for catastrophic future.”  The opening of Bradbury’s article is to the point: 

It’s past time to tell the truth about the state of the world’s coral reefs, the nurseries of tropical coastal fish stocks.  They have become zombie ecosystems, neither dead nor truly alive in any functional sense, and on a trajectory to collapse within a human generation.  There will be remnants here and there, but the global coral reef ecosystem — with its storehouse of biodiversity and fisheries supporting millions of the world’s poor — will cease to be.

3c. Arctic carbon stores

As Climate Progress recently noted: “We’ve known for a while that ‘permafrost’ was a misnomer” because thawing permafrost feedback will turn the Arctic from a net carbon sink to a net source in the 2020s and defrosting permafrost will likely add up to 1 ºC to total global warming by 2100.   A 2012 UNEP report on policy implications of warming permafrost says the recent observations “indicate that large-scale thawing of permafrost may have already started.”  In February 2013, scientists using radiometric dating techniques on Russian cave formations to measure historic melting rates warned that a +1.5 ºC global rise in temperature compared to pre-industrial was enough to start a general permafrost melt.  Vaks, Gutareva et al. found that “global climates only slightly warmer than today are sufficient to thaw extensive regions of permafrost.” Vaks says that: “1.5 ºC appears to be something of a tipping point.”

Previously a study of East Siberian permafrost by Khvorostyanov, Ciais et al.  found that once mobilised, the process would be self-maintaining due to “deep respiration and methanogenesis” (formation of methane by microbes).  In other words, the microbial action that produces methane as the carbon stores melt would produce sufficient heat to maintain the process: “once active layer deepening in response to atmospheric warming is enough to trigger deep-soil respiration, and soil microorganisms are activated to produce enough heat, the mobilization of soil carbon can be very strong and self-sustainable.”

A sharp scientific debate has started on the stability of large methane clathrate stores just below the ocean floor on the shallow East Siberian Sea, following the publication in July 2013 of research by Whiteman, Hope and Wadhams which said that the release of a single giant “pulse” of methane from thawing Arctic permafrost beneath the East Siberian Sea could come with a $60 trillion global price tag. Wadhams says “the loss of sea ice leads to seabed warming, which leads to offshore permafrost melt, which leads to methane release, which leads to enhanced warming, which leads to even more rapid uncovering of seabed,” and this is not “a low probability event.”

Multiple targets reduce allowable warming

Steinacher, Joos et al. explore the interaction of targets in emissions reductions, focusing on the 2 ºC temperature goal. They find that when multiple climate targets are set (such as food production capacity, ocean acidity, atmospheric temperature), “allowable cumulative emissions are greatly reduced from those inferred from the temperature target alone.” In fact, “When we consider all targets jointly, CO2 emissions have to be cut twice as much as if we only want to meet the 2 ºC target.”

Lessons from climate history

Another fruitful line of inquiry on whether climate change is already “dangerous” is to look at the paleo-climate (climate history) record for circumstances analogous to present conditions to learn what planetary and climate conditions were like at that time.  With current CO2 levels at 400 ppm, a useful comparison is the Pliocene (3–5 million years ago).  The research body is large and growing in this area, but here are some examples:

Sea-levels

Rohling, Grant et al.  find that during the mid-Pliocene, when greenhouse gases were similar to today, sea levels were more than 20 metres higher than today “we estimate sea level for the Middle Pliocene epoch (3.0–3.5 Myr ago) – a period with near-modern CO2 levels – at 25 ±5 metres above present, which is validated by independent sea-level data.” Likewise Hansen, Sato et al. find that “during the middle-Pliocene… we find sea level fluctuations of 20–40 metres associated with global temperature variations between today’s temperature and +3 °C.”

Speed of sea-level rise

The speed of sea-level rise may far exceed the current, rather reticent estimates that are used for policy purposes.  Blancon, Eisenhauer et al. examined the paleo-climate record and showed a sea-level rises of 3 metres in 50 years due to the rapid melting of ice sheets 123,000 years ago in the Eemian, when the energy imbalance in the climate system was less than at present. 

Polar feedbacks

Hansen, Sato et al. find that current temperatures are at least as high as the Holocene Maximum (i.e., as high as they have been over the last 10,000 years).  They sum up: 

Earth at peak Holocene temperature is poised such that additional warming instigates large amplifying high-latitude feedbacks.  Mechanisms on the verge of being instigated include loss of Arctic sea ice, shrinkage of the Greenland ice sheet, loss of Antarctic ice shelves, and shrinkage of the Antarctic ice sheets.  These are not runaway feedbacks, but together they strongly amplify the impacts in polar regions of a positive (warming) climate forcing…  Augmentation of peak Holocene temperature by even +1 ºC would be sufficient to trigger powerful amplifying polar feedbacks, leading to a planet at least as warm as in the Eemian and Holsteinian periods, making ice sheet disintegration and large sea level rise inevitable.

[It is relevant here to note that warming in the pipeline due to thermal inertia, plus warming associated with the loss of aerosols, is greater than +1ºC.]

And during the Pliocene, with atmospheric greenhouse levels similar to today, the northern hemisphere was free of glaciers and ice sheets and beech trees grew in the Transantarctic Mountains. There are also strong indications that permanent El Nino conditions prevailed.

4d. Arctic carbon stores

As discussed above, scientists using radiometric dating techniques on Russian cave formations to measure historic melting rates going back 500,000 years conclude that a +1.5 ºC global rise in temperature compared to pre-industrial is enough to initiate widespread permafrost melt.  

In May this year, Brigham-Grette, Melles et al. published evidence from Lake El’gygytgyn, in north-east Arctic Russia, showing that 3.6–3.4 million years ago, summer mid-Pliocene temperatures locally were ~8 °C warmer than today, when CO2 was ~400 ppm.  This is highly significant because researchers including Celia Bitz and Philippe Ciais have previously found that the tipping point for the large-scale loss of permafrost carbon is around +8 ºC  to 10 ºC regional temperature increase.  Caias told the March 2009 Copenhagen climate science conference that: “A global average increase in air temperatures of +2 ºC and a few unusually hot years could see permafrost soil temperatures reach the +8 ºC threshold for releasing billions of tonnes of carbon dioxide and methane.” So, if the current level of greenhouse gases is enough to produce Arctic regional warming of ~+8 °C and that is a likely tipping point for large-scale permafrost loss, we have reached a disturbing milestone.

Even more disturbing is new research from Ballantyne, Axford et al. which says that during the Pliocene epoch, when CO2 levels were ~400 ppm, Arctic surface temperatures were 15–20 °C warmer than today’s surface temperatures. They suggest that much of the surface warming likely was due to ice-free conditions in the Arctic. Compared to the estimated tipping point for the large-scale loss of permafrost carbon of +8 ºC to 10 ºC regional warming, this research confirms both that the current level of greenhouse gases is sufficient to create both a sea-ice-free Arctic and Arctic warming more than sufficient to trigger large-scale loss of permafrost carbon.

Next post: Climate safety and the emissions reduction challenge 

http://www.climatecodered.org/2013/09/is-climate-change-already-dangerous-3.html 

James Hansen: Doubling Down on Our Faustian Bargain

by James Hansen, Pushker Kharecha and Makiko Sato, Huffington Post, March 31, 2013

Humanity's Faustian climate bargain is well known. Humans have been pumping both greenhouse gases (mainly CO2) and aerosols (fine particles) into the atmosphere for more than a century. The CO2 accumulates steadily, staying in the climate system for millennia, with a continuously increasing warming effect. Aerosols have a cooling effect (by reducing solar heating of the ground) that depends on the rate that we pump aerosols into the air, because they fall out after about five days.

Aerosol cooling probably reduced global warming by about half over the past century, but the amount is uncertain because global aerosols and their effect on clouds are not measured accurately. Aerosols increased rapidly after World War II as fossil fuel use increased ~5%/year with little pollution control (Fig. 1). Aerosol growth slowed in the 1970s with pollution controls in the U.S. and Europe, but accelerated again after ~2000.

Fig. 1. CO2 annual emissions from fossil fuel use and cement manufacture, update of a figure using recent data.
Fig. 2. Annual increase of CO2 at Mauna Loa. The 12-month running mean reduces the double noise in the 12-month change. Blue asterisks show the end-of-year 12-month change often reported in the media.

The rapid growth of fossil fuel CO2 emissions in the past decade is mainly from increased coal use (Fig. 1), mostly in China with little control of aerosol emissions. It is thus likely that there has been an increase in the negative (cooling) climate forcing by aerosols in the past decade, as suggested by regional aerosols measurements in the Far East, but until proper global aerosol monitoring is initiated, as discussed below, the aerosol portion of the amplified Faustian bargain remains largely unquantified.

In our current paper we describe another component to the fossil fuel Faustian bargain, which is suggested by a careful look at observed atmospheric CO2 change (Fig. 2). The orange curve in Fig. 2 is the 12-month change of CO2 at Mauna Loa. This curve is quite "noisy," in part because it has double noise, being affected by short-term variability at both the start-point and end-point in taking the 12-month difference in CO2 amount. A more meaningful measure of the CO2 growth is provided by the 12-month running mean (red curve in Fig. 2). The temporal variability of the red curve has physical significance, most of the variability being accounted for by the Southern (El Nino-La Nina) Oscillation and the Pinatubo volcanic eruption in the early 1990s, as discussed in our paper.

NOAA recently reported the second largest annual CO2 increase in their Mauna Loa record. What they report is the end-of-year change in the noisy orange curve, the end-of-year values being indicated by blue asterisks in Fig. 2. It is practically certain that still larger CO2 increases will soon be reported, because of the huge increase of the rate of fossil fuel CO2 emissions in the past decade (black curve in Fig. 1), indeed we must expect reports of annual CO2 increases exceeding 3 ppm CO2.

An interesting point, however, is the failure of the observed increases in atmospheric CO2 to increase as rapidly as the fossil fuel source has increased. This fact is contrary to suggestions that terrestrial and ocean carbon sinks are tending to saturate as CO2 emissions continue.

An informative presentation of CO2 observations is the ratio of annual CO2 increase in the air divided by annual fossil fuel CO2 emissions, the "airborne fraction" (Fig. 3, right scale). This airborne fraction, clearly, is not increasing. Thus the net ocean plus terrestrial sink for carbon emissions has increased by a factor of 3 to 4 since 1958, accommodating the emissions increase by that factor.

Fig. 3. Fossil fuel CO2 emissions (left scale) and airborne fraction, i.e., the ratio of observed atmospheric CO2 increase to fossil fuel CO2 emissions. Final three values are 5-, 3- and 1-year means.

Remarkably, the airborne fraction has declined since 2000. The seven-year running mean had remained close to 60% up to 2000, except for the period affected by Pinatubo. The airborne fraction is affected by factors other than the efficiency of carbon sinks, most notably by changes in the rate of fossil fuel emissions. However, the change of emission rate in 2000 from 1.5%/year to 3.1%/year (Fig. 1), other things being equal, would have caused a sharp increase of the airborne fraction (because a rapid source increase provides less time for carbon to be moved downward out of the ocean's upper layers). A decrease in land use emissions during the past decade might contribute a partial explanation for the decrease of the airborne fraction, but something more than land use change seems to be occurring.

We suggest that the surge of fossil fuel use, mainly coal, since 2000 is a basic cause of the large increase of carbon uptake by the combined terrestrial and ocean carbon sinks. One mechanism by which fossil fuel emissions increase carbon uptake is by fertilizing the biosphere via provision of nutrients essential for tissue building, especially nitrogen, which plays a critical role in controlling net primary productivity and is limited in many ecosystems. Modeling and field studies confirm a major role of nitrogen deposition, working in concert with CO2 fertilization, in causing a large increase in net primary productivity of temperate and boreal forests. A plausible addition of 5 TgN/year from fossil fuels and net ecosystem productivity of 200 kgC per kgN16 yields an annual carbon drawdown of 1 GtC/year, which is of the order of what is needed to explain the post-2000 anomaly in airborne CO2.

Independent of a possible aerosol effect on the carbon cycle, it is known that aerosols are an
important climate forcing. IPCC17 concludes that aerosols are a negative (cooling) forcing, probably between -0.5 and -2.5 W/m². Hansen et al., based mainly on analysis of Earth's energy imbalance, derive an aerosol forcing -1.6 ± 0.3 W/m², consistent with an analysis of Murphy et al. that suggests an aerosol forcing about -1.5 W/m². This large negative aerosol forcing reduces the net climate forcing of the past century by about half.

Reduction of the net human-made climate forcing by aerosols has been described as a "Faustian bargain," because the aerosols constitute deleterious particulate air pollution. Reduction of the net climate forcing by half will continue only if we allow air pollution to build up to greater and greater amounts. More likely, humanity will demand and achieve a reduction of particulate air pollution, whereupon, because the CO2 from fossil fuel burning remains in the surface climate system for millennia, the "devil's payment" will be extracted from humanity via increased global warming.

So is the new data we present here good news or bad news, and how does it alter the "Faustian bargain"? At first glance there seems to be some good news. First, if our interpretation of the data is correct, the surge of fossil fuel emissions, especially from coal burning, along with the increasing atmospheric CO2 level is "fertilizing" the biosphere, and thus limiting the growth of atmospheric CO2. Also, despite the absence of accurate global aerosol measurements, it seems that the aerosol cooling effect is probably increasing based on evidence of aerosol increases in the Far East.

Both effects work to limit global warming and thus help explain why the rate of global warming seems to be less this decade than it has been during the prior quarter century. This data interpretation also helps explain why multiple warnings that some carbon sinks are "drying up" and could even become carbon sources, e.g., boreal forests infested by pine bark beetles and the Amazon rain forest suffering from drought, have not produced an obvious impact on atmospheric CO2.

However, increased CO2 uptake does not necessarily mean that the biosphere is healthier or that the increased carbon uptake will continue indefinitely. Nor does it change the basic facts about the potential magnitude of the fossil fuel carbon source and the long lifetime of fossil fuel CO2 in the surface carbon reservoirs (atmosphere, ocean, soil, biosphere) once the fossil fuels are burned. Fertilization of the biosphere affects the distribution of the fossil fuel carbon among these reservoirs, at least on the short run, but it does not alter the fact that the fossil carbon will remain in these reservoirs for millennia.

The principal implication of our present analysis relates to the Faustian bargain. Increased short-term masking of greenhouse gas warming by fossil fuel particulate and nitrogen pollution is a "doubling down" of the Faustian bargain, an increase in the stakes. The more we allow the Faustian debt to build, the more unmanageable the eventual consequences will be. Yet globally there are plans to build more than 1,000 coal-fired power plants and plans to develop some of the dirtiest oil sources on the planet. These plans should be vigorously resisted. We are already in a deep hole -- it is time to stop digging.

The tragedy of this science story is that the great uncertainty in interpretations of the climate forcings did not have to be. Global aerosol properties should be monitored to high precision, similar to the way CO2 is monitored. The capability of measuring detailed aerosol properties has long existed, as demonstrated by observations of Venus. The requirement is measurement of the polarization of reflected sunlight to an accuracy of 0.1%, with measurements covering the spectral range from near ultraviolet to the near-infrared at a range of scattering angles, as is possible from an orbiting satellite. Unfortunately, the satellite mission designed for that purpose failed to achieve orbit, suffering precisely the same launch failure as the Orbiting Carbon Observatory (OCO). Although a replacement OCO mission is in preparation, no replacement aerosol mission is scheduled.

http://www.huffingtonpost.com/dr-james-hansen/doubling-down-on-our-faustian-bargain_b_2989535.html

What happened to greenhouse warming during mid-century cooling? by John Cook, Skeptical Science

What happened to greenhouse warming during mid-century cooling?

by John Cook, Skeptical Science, July 3, 2010

A few weeks back while researching global brightening, I came across a gem of a paper: Impact of Global brightening and dimming on global warming (Wild et al. 2007). The paper examines temperature trends over the second half of the 20th Century, including the cooling period in the middle of the century. From the 1950s to early 1980s, while CO2 levels were rising, global temperatures cooled slightly. How can this be if CO2 causes warming? Wild et al. found there was greenhouse warming during this cooling period, and they find it in an interesting place...

The paper looks at trends in the amount of sunlight reaching the ground over the latter 20th century. Various factors can affect how much sunlight gets through to the Earth's surface, with the amount of aerosols in the atmosphere being the main contributor. And of course, the amount of sunlight reaching the surface will have an effect on global temperatures. Wild et al. (2007) attempt to disentangle just how much contribution this surface dimming and brightening has on global temperature.

They start by looking at measurements of surface radiation from 1958 (when widespread measurements began). They find a period of "global dimming" from 1958 to 1990 where surface radiation fell. Afterwards, the dimming levels off and transitions to slight brightening from 1985 to 2002. While the warming during the period of solar dimming is moderate, the warming is more rapid in the last two decades where dimming was no more present.


Temperature change over global land surfaces from 1958 to 2002.
 
How much does global dimming and brightening contribute to the temperature trends? To disentangle the effects of dimming and brightening from greenhouse warming, Wild et al. dig a little deeper into the temperature record by looking at the daily temperature cycle. Sunlight affects the daily maximum temperature more than the nightly minimum, which is affected more by the greenhouse effect. What they find is from 1958 to 1985, during global dimming, the maximum daytime temperature falls. This makes sense as less sunlight is reaching and warming the Earth's surface. The interesting result is that over this period, the nighttime minimum temperature increases. While global dimming was cooling temperatures in the daytime, the increased greenhouse effect was warming in the nighttime.

From 1985 to 2002, the warming trend during the daytime increases significantly and almost catches up to the nighttime warming trend (almost but not quite). This is consistent with the surface radiation measurements which find global dimming levels off or transitions to brightening in the mid 1980s. Global dimming masked greenhouse warming until the 1980s. Once the atmosphere cleared and the dimming was removed, global warming came into its own.

Does this mean global brightening could be responsible for global warming? Not quite. While there has been some global brightening since 1985, the amount of sunlight hitting the Earth hasn't reached 1960 levels yet. Sunlight has fallen since 1960 while global temperatures have risen 0.8 °C. The daily temperature cycle indicates its greenhouse warming that has driven the warming. Yet another human fingerprint!

Where did CO2 warming go during mid-century cooling? Global dimming caused by pollution masked the increased greenhouse effect. Nevertheless, the CO2 warming was still percolating away while we were sleeping.

Link:  http://www.skepticalscience.com/What-happened-to-greenhouse-warming-during-mid-century-cooling.html

Australian Dept. of Climate Change report: Faster Change & More Serious Risks by Will Steffen

Dorothy Cutting, Director, West Coast Climate Equity, sent the link to this 60-page pdf file, which is a report by the Australian Government Department of Climate Change, entitled:

Climate Change 2009:
Faster Change & More Serious Risks
by Will Steffen

This is what she had to say:

"This is a stunning report. How unnerving it is to see climate data from a different perspective; there are so many slides so new to me. A picture being well worth what it is, I’m stalled on the shocking image of projected temperature anomalies in France, the Ukraine and the Sahel. I’ve seen the numbers, of course, but this slide gives this data so much more impact."

Page 5, Figure 1c shows sea level rise.

Page 6, Figure 2a shows rising CO2 correlated with decreasing sea ice.

Lots of figures showing increasing temperatures and droughts.

Figure 23 shows the projected summer temperatures for various geographic locations, like Europe and the Ukraine -- not pleasant reading at all.

From page 32:

"Some of the most striking advances in climate change science over the past three to four years have been made by taking a systems perspective, in which interactions among components of the climate system and feedback processes that highlight potentially important second-order effects have been elucidated.
An example is research on the links between climate change and the Hadley Circulation, and the
implications of these links for storm tracks, regional precipitation patterns, and modes of natural variability such as the El Niño – Southern Oscillation (Frierson et al. 2007; Lu et al. 2008; Seidel et al. 2008). Much of this new work points in the same direction – that as the 21st century progresses, system-level effects will increasingly amplify rather than dampen the human
perturbation of the climate system."

Page 33, Figure 37 shows the Northern Hemisphere and geographic concentrations of permafrost -- yikes!

Anyway, my words cannot describe all of the very well-portrayed information in the many figures. The report is highly readable -- just takes a bit to download, but well worth it.

This report tells it all, very clearly.

R.C. Moffet & K.A. Prather: In-situ measurements of the mixing state and optical properties of soot with implications for radiative forcing estimates

Proceedings of the National Academy of Sciences, published online before print July 6, 2009; doi: 10.1073/pnas.0900040106

In-situ measurements of the mixing state and optical properties of soot with implications for radiative forcing estimates

Ryan C. Moffet (Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, U.S.A.) and Kimberly A. Prather* (Department of Chemistry and Biochemistry, University of California, San Diego, and Scripps Institute of Oceanography, La Jolla, CA 92093, U.S.A.)

Edited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved May 29, 2009 (received for review January 10, 2009).

Abstract

Our ability to predict how global temperatures will change in the future is currently limited by the large uncertainties associated with aerosols. Soot aerosols represent a major research focus as they influence climate by absorbing incoming solar radiation resulting in a highly uncertain warming effect. The uncertainty stems from the fact that the actual amount soot warms our atmosphere strongly depends on the manner and degree in which it is mixed with other species, a property referred to as mixing state. In global models and inferences from atmospheric heating measurements, soot radiative forcing estimates currently differ by a factor of 6, ranging between 0.2–1.2 W/m², making soot second only to CO₂ in terms of global warming potential. This article reports coupled in situ measurements of the size-resolved mixing state, optical properties, and aging timescales for soot particles. Fresh fractal soot particles dominate the measured absorption during peak traffic periods (6–9 a.m. local time). Immediately after sunrise, soot particles begin to age by developing a coating of secondary species including sulfate, ammonium, organics, nitrate, and water. Based on these direct measurements, the core-shell arrangement results in a maximum absorption enhancement of 1.6× over fresh soot. These atmospheric observations help explain the larger values for soot forcing measured by others and will be used to obtain closure in optical property measurements to reduce one of the largest remaining uncertainties in climate change.

• *Correspondence e-mail: kprather@ucsd.edu

• Author contributions: R.C.M. and K.A.P. designed research, performed research, analyzed data, and wrote the paper. The authors declare no conflict of interest.

Link to abstract: http://www.pnas.org/content/early/2009/07/02/0900040106.abstract

K. Wang, R. E. Dickinson & S. Liang, Science, 323, Clear sky visibility has decreased over land globally from 1973 to 2007

Science, 13 March 2009, Vol. 323, No. 5920, pp. 1468-1470; DOI: 10.1126/science.1167549

Clear Sky Visibility Has Decreased over Land Globally from 1973 to 2007

Kaicun Wang,^1* Robert E. Dickinson,² and Shunlin Liang¹

Abstract

Visibility in the clear sky is reduced by the presence of aerosols, whose types and concentrations have a large impact on the amount of solar radiation that reaches Earth's surface. Here we establish a global climatology of inverse visibilities over land from 1973 to 2007 and interpret it in terms of changes in aerosol optical depth and the consequent impacts on incident solar radiation. The aerosol contribution to "global dimming," first reported in terms of strong decreases in measured incident solar radiation up to the mid-1980s, has monotonically increased over the period analyzed. Since that time, visibility has increased over Europe, consistent with reported European "brightening," but has decreased substantially over south and east Asia, South America, Australia, and Africa, resulting in net global dimming over land.

¹ Department of Geography, University of Maryland, College Park, MD 20742, USA.
² Department of Geological Sciences, University of Texas, Austin, TX 78712, USA.

^* To whom correspondence should be addressed. e-mail: kcwang@umd.edu

Link to abstract: http://www.sciencemag.org/cgi/content/abstract/323/5920/1468

Global dimming -- Aerosol pollution dims skies as well as befouling the air

Pollution dims skies as well as befouling the air

Reuters – Cars and tricycles can be seen along a road on a hazy day in central Beijing March 4, 2009. In recent …

WASHINGTON, March 12, 2009, Yahoo! News – The skies are dimming, for most of the world. Increases in airborne pollution have dimmed the skies by blocking sunlight over the past 30 years, researchers report in Friday's edition of the journal Science.

While decreases in atmospheric visibility — known as global dimming — have been reported in the past, the new study compiles satellite and land-based data for a longer period than had been available.

"Creation of this database is a big step forward for researching long-term changes in air pollution and correlating these with climate change," Kaicun Wang, assistant research scientist in the University of Maryland, said in a statement. "And it is the first time we have gotten global long-term aerosol information over land to go with information already available on aerosol measurements over the world's oceans."

They reported that dimming is occurring everywhere except Europe, where declines in pollution have resulted in brighter skies.

Changes in aerosols can affect weather and also may have an impact on climate, though past studies have been inconclusive. These pollutants can result in cooling by reflecting sunlight back into space, but they also can absorb solar energy, warming the atmosphere.

Researchers at the National Oceanic and Atmospheric Administration, meanwhile, warned that suggestions for a high-atmosphere "sunshade" of particles to battle global warming could reduce energy production from solar power plants.

Those proposals are aimed at blocking sunlight that can be absorbed by so-called greenhouse gases like carbon dioxide, warming climate.

But airborne particles also scatter light that does get through, and that diffuse light cannot be used by solar energy concentrating systems that produce electricity, Daniel Murphy, a scientist at NOAA's Earth System Research Laboratory in Boulder, Colo., reported in the journal Environmental Science and Technology.

Flat photovoltaic and hot water panels, commonly seen on household roofs, use both diffuse and direct sunlight, so they would be less affected.

Science: http://www.sciencemag.org

NOAA: http://www.noaa.gov

Environmental Science and Technology: http://pubs.acs.org/journal/esthag?cookieSet1

R. Vautard, P. Yiou & G. J. v. Oldenborgh: Decline of fog, mist and haze in Europe over the past 30 years (global dimming)

Letter abstract

Nature Geoscience, published online: 18 January 2009 | doi:10.1038/ngeo414

Decline of fog, mist and haze in Europe over the past 30 years

Robert Vautard¹, Pascal Yiou¹ and Geert Jan van Oldenborgh²

Abstract

Surface solar radiation has undergone decadal variations since the middle of the twentieth century, producing global 'dimming' and 'brightening' effects [1, 2.] These variations presumably result from changes in aerosol burden and clouds[3], but the detailed processes involved have yet to be determined. Over Europe, the marked solar radiation increase since the 1980s is thought to have contributed to the observed large continental warming[4], but this contribution has not been quantified. Here we analyse multidecadal data of horizontal visibility, and find that the frequency of low-visibility conditions such as fog, mist and haze has declined in Europe over the past 30 years, for all seasons and all visibility ranges between distances of 0 and 8 km. This decline is spatially and temporally correlated with trends in sulphur dioxide emissions, suggesting a significant contribution of air-quality improvements. Statistically linking local visibility changes with temperature variations, we estimate that the reduction in low-visibility conditions could have contributed on average to about 10–20% of Europe's recent daytime warming and to about 50% of eastern European warming. Large improvements in air quality and visibility already achieved in Europe over the past decades may mean that future reductions in the frequency of low-visibility events will be limited, possibly leading to less rapid regional warming.

1. LSCE/IPSL, laboratoire CEA/CNRS/UVSQ, 91191 Gif sur Yvette Cedex, France
2. KNMI, PO Box 201, 3730 AE De Bilt, The Netherlands

Correspondence to: Robert Vautard¹ e-mail: robert.vautard@cea.fr

Link to article: http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo414.html

Global dimming: Clearer skies in Europe added to warming

Clearer skies in Europe added to warming

January 18th, 2009 in physorg.com

Sheep graze on a meadow near Munich as the sun sets. Fog, mist and haze in Europe have declined over the last three decades, a trend that may have stoked regional warming and ironically could be linked to better air quality, a study published on Sunday says.

Fog, mist and haze in Europe have declined over the last three decades, a trend that may have stoked regional warming and ironically could be linked to better air quality, a study published on Sunday says.

From 1978-2006, temperatures in parts of Europe rose above the global land average, with prominent increases in the north, centre and eastern parts of the continent.

As much as 20% of Europe's warming during this time, according to the study, can be pinned on a reduction in fog, mist and haze, which -- because they are white -- reflect solar radiation and thus keep the ground cool.

In eastern Europe, the decline in fog, mist and haze could account for 50%, the paper believes.

The authors, led by Robert Vautard of France's Atomic Energy Commission (CEA), pored over data from 342 weather stations around Europe.

They found that over nearly 30 years, the number of days categorised as having restricted visibility fell by half. These categories were determined by ranges of visibility at 2, 5, and 8 km (1.2, 3, and 5 miles, respectively).

The phenomenon is closely linked to falling levels of atmospheric sulphur dioxide (SO2), a byproduct of burning oil and coal that causes notorious "acid rain" that damages forests and lakes.

The temperature rise has been especially perceptible in Eastern Europe, where the end of the Communist system closed down innumerable sources of coal pollution.

However, the SO2 cleanup is now largely tapering off.

This means the fog reduction will probably stop and "the warming trend in Europe will not be so large in the coming years," Vautard told AFP.

According to the Intergovernmental Panel on Climate Change (IPCC) -- the UN's paramount authority on global warming -- the global average temperature rose 0.74 °C (1.33 °F) from 1906-2005, and the pace in the last 50 years was double that of the first half-century.

A blanket of fog can reduce local temperatures by some 2 °C (3.6 °F), according to figures quoted in the new study.

Link to article: http://www.physorg.com/news151522638.html

Global Dimming report by the BBC

Blog reader Leon has given me the link to the video report on "global dimming," and it is a must-see for all those seeking a better understanding of the problems we need to confront:

http://video.google.com/videoplay?docid=-2058273530743771382