The terrible truth of climate change

by Joëlle Gergis, The Monthly, 2019

The latest science is alarming, even for climate scientists

In June, I delivered a keynote presentation on Australia’s vulnerability to climate change and our policy challenges at the annual meeting of the Australian Meteorological and Oceanographic Society, the main conference for those working in the climate science community. I saw it as an opportunity to summarize the post-election political and scientific reality we now face.

As one of the dozen or so Australian lead authors on the United Nations Intergovernmental Panel on Climate Change’s (IPCC) 6th Assessment Report, currently underway, I have a deep appreciation of the speed and severity of climate change unfolding across the planet. Last year I was also appointed as one of the scientific advisers to the Climate Council, Australia’s leading independent body providing expert advice to the public on climate science and policy. In short, I am in the confronting position of being one of the few Australians who sees the terrifying reality of the climate crisis.

Preparing for this talk I experienced something gut-wrenching. It was the realization that there is now nowhere to hide from the terrible truth.

The last time this happened to me, I was visiting my father in hospital following emergency surgery for a massive brain haemorrhage. As he lay unconscious in intensive care, I examined his CT scan with one of the attending surgeons who gently explained that the dark patch covering nearly a quarter of the image of his brain was a pool of blood. Although they had done their best to drain the area and stem the bleeding, the catastrophic nature of the damage was undeniable. The brutality of the evidence was clear – the full weight of it sent my stomach into freefall.

The results coming out of the climate science community at the moment are, even for experts, similarly alarming.

One common metric used to investigate the effects of global warming is known as “equilibrium climate sensitivity,” defined as the full amount of global surface warming that will eventually occur in response to a doubling of atmospheric CO2 concentrations compared to pre-industrial times. It’s sometimes referred to as the holy grail of climate science because it helps quantify the specific risks posed to human society as the planet continues to warm.

We know that CO2 concentrations have risen from pre-industrial levels of 280 parts per million (ppm) to approximately 410 ppm today, the highest recorded in at least three million years. Without major mitigation efforts, we are likely to reach 560 ppm by around 2060.

When the IPCC’s 5th Assessment Report was published in 2013, it estimated that such a doubling of CO2 was likely to produce warming within the range of 1.5 to 4.5 °C as the Earth reaches a new equilibrium. However, preliminary estimates calculated from the latest global climate models (being used in the current IPCC assessment, due out in 2021) are far higher than with the previous generation of models. Early reports are predicting that a doubling of CO2 may in fact produce between 2.8 and 5.8 °C of warming. Incredibly, at least 8 of the latest models produced by leading research centers in the United States, the United Kingdom, Canada and France are showing climate sensitivity of 5 °C or warmer.

When these results were first released at a climate modelling workshop in March this year, a flurry of panicked emails from my IPCC colleagues flooded my inbox. What if the models are right? Has the Earth already crossed some kind of tipping point? Are we experiencing abrupt climate change right now?

The model runs aren’t all available yet, but when many of the most advanced models in the world are independently reproducing the same disturbing results, it’s hard not to worry.

When the UN’s Paris Agreement was adopted in December 2015, it defined a specific goal: to keep global warming to well below 2 °C and as close as possible to 1.5 °C above pre-industrial levels (defined as the climate conditions experienced during the 1850–1900 period). While admirable in intent, the agreement did not impose legally binding limits on signatory nations and contained no enforcement mechanisms. Instead, each country committed to publicly disclosed Nationally Determined Contributions (NDCs) to reduce emissions. In essence, it is up to each nation to act in the public interest.

Even achieving the most ambitious goal of 1.5 °C will see the further destruction of between 70 and 90% of reef-building corals compared to today, according to the IPCC’s “Special Report on Global Warming of 1.5 °C,” released last October. With 2 °C of warming, a staggering 99% of tropical coral reefs disappear. An entire component of the Earth’s biosphere – our planetary life support system – would be eliminated. The knock-on effects on the 25% of all marine life that depends on coral reefs would be profound and immeasurable.

So how is the Paris Agreement actually panning out?

In 2017, we reached 1 °C of warming above global pre-industrial conditions. According to the UN Environment Program’s “Emissions Gap Report,” released in November 2018, current unconditional NDCs will see global average temperature rise by 2.9 to 3.4 °C above pre-industrial levels by the end of this century.

To restrict warming to 2 °C above pre-industrial levels, the world needs to triple its current emission reduction pledges. If that’s not bad enough, to restrict global warming to 1.5 °C, global ambition needs to increase five-fold.

Meanwhile, the Australian federal government has a target of reducing emissions by 26 to 28% below 2005 levels by 2030, which experts believe is more aligned with global warming of 3 to 4 °C. Despite Prime Minister Scott Morrison’s claim that we will meet our Paris Agreement commitments “in a canter,” the UNEP report clearly identifies Australia as one of the G20 nations that will fall short of achieving its already inadequate NDCs by 2030.

Even with the 1 °C of warming we’ve already experienced, 50% of the Great Barrier Reef is dead. We are witnessing catastrophic ecosystem collapse of the largest living organism on the planet. As I share this horrifying information with audiences around the country, I often pause to allow people to try and really take that information in.

Increasingly after my speaking events, I catch myself unexpectedly weeping in my hotel room or on flights home. Every now and then, the reality of what the science is saying manages to thaw the emotionally frozen part of myself I need to maintain to do my job. In those moments, what surfaces is pure grief. It’s the only feeling that comes close to the pain I felt processing the severity of my dad’s brain injury. Being willing to acknowledge the arrival of the point of no return is an act of bravery.

But these days my grief is rapidly being superseded by rage. Volcanically explosive rage. Because in the very same IPCC report that outlines the details of the impending apocalypse, the climate science community clearly stated that limiting warming to 1.5 °C is geophysically possible.

Past emissions alone are unlikely to raise global average temperatures to 1.5 °C above pre-industrial levels. The IPCC report states that any further warming beyond the 1 °C already recorded would likely be less than 0.5 °C over the next 20 to 30 years, if all anthropogenic greenhouse gas emissions were reduced to zero immediately. That is, if we act urgently, it is technically feasible to turn things around. The only thing missing is strong global policy.

Although the very foundation of human civilization is at stake, the world is on track to seriously overshoot our UN targets. Worse still, global carbon emissions are still rising. In response, scientists are prioritizing research on how the planet has responded during other warm periods in the Earth’s history.

The most comprehensive summary of conditions experienced during past warm periods in the Earth’s recent history was published in June 2018 in one of our leading journals, Nature Geoscience, by 59 leading experts from 17 countries. The report concluded that warming of between 1.5 and 2 °C in the past was enough to see significant shifts in climate zones, and land and aquatic ecosystems “spatially reorganize.”

These changes triggered substantial long-term melting of ice in Greenland and Antarctica, unleashing 6 to 13 meters of global sea-level rise lasting thousands of years.

Examining the Earth’s climatic past tells us that even between 1.5 and 2 °C of warming sees the world reconfigure in ways that people don’t yet appreciate. All bets are off between 3 and 4 °C, where we are currently headed. Parts of Australia will become uninhabitable, as other areas of our country become increasingly ravaged by extreme weather events.

This year the Australian Meteorological and Oceanographic Society’s annual conference was held in Darwin, where the infamous Cyclone Tracy struck on Christmas Day in 1974, virtually demolishing the entire city. More than 70% of the city’s buildings, including 80% of its houses, were destroyed. Seventy-one people were killed and most of the 48,000 residents made homeless. Conditions were so dire that around 36,000 people were evacuated, many by military aircraft. It was a disaster of monumental proportions.

As I collated this information for my presentation, it became clear to me that Cyclone Tracy is a warning. Without major action, we will see tropical cyclones drifting into areas on the southern edge of current cyclone zones, into places such as southeast Queensland and northern New South Wales, where infrastructure is not ready to cope with cyclonic conditions.

These areas currently house more than 3.6 million people; we simply aren’t prepared for what is upon us.

There is a very rational reason why Australian schoolkids are now taking to the streets – the immensity of what is at stake is truly staggering. Staying silent about this planetary emergency no longer feels like an option for me either. Given how disconnected policy is from scientific reality in this country, an urgent and pragmatic national conversation is now essential. Otherwise, living on a destabilized planet is the terrible truth that we will all face.

As a climate scientist at this fraught point in our history, the most helpful thing I can offer is the same professionalism that the doctor displayed late that night in Dad’s intensive-care ward. A clear-eyed and compassionate look at the facts.

We still have time to try and avert the scale of the disaster, but we must respond as we would in an emergency. The question is, can we muster the best of our humanity in time?

Joëlle Gergis

Joëlle Gergis is an award-winning climate scientist and writer based at the Australian National University. She is the author of Sunburnt Country: The History and Future of Climate Change in Australia.

© 2019 The Monthly. All rights reserved.

https://www.themonthly.com.au/issue/2019/august/1566136800/jo-lle-gergis/terrible-truth-climate-change

Climate Code Red: What we learned about the climate system in 2017 that should send shivers down the spines of policy makers

by David Spratt, Climate Code Red, January 15, 2018

Much of what happened in 2017 was predictable: news of climate extremes became, how can I put it … almost the norm. There was record-breaking heat on several continents, California’s biggest wildfire (extraordinarily in the middle of winter), an ex-tropical cyclone hitting Ireland (yes, Ireland) in October, and the unprecedented Hurricanes Harvey, Irma and Maria that swept through the Atlantic in August. The US government agency, the NOAA, reported that there were 16 catastrophic billion-dollar weather/climate events in the USA during 2017.

And 2017 “marks the first time some of the (scientific) papers concluded that an event could not have occurred — like, at all — in a world where global warming did not exist. The studies suggested that the record-breaking global temperatures in 2016, an extreme heat wave in Asia and a patch of unusually warm water in the Alaskan Gulf were only possible because of human-caused climate change,” Reuters reported.

At both poles, the news continues to be not good. At the COP23 in Bonn, Pam Pearson, Founder and Director of the International Cryosphere Climate Initiative, warned that the cryoshere is becoming “an irreversible driver of climate change.” She said that most cryosphere thresholds are determined by peak temperature, and the length of time spent at that peak, warning that “later, decreasing temperatures after the peak are largely irrelevant, especially with higher temperatures and longer duration peaks.” Thus “overshoot scenarios,” which are now becoming the norm in policy-making circles (including all 1.5 °C scenarios) hold much greater risks.

As well, Pearson said that 2100 is a misleading and minimizing measure of cryosphere response: “When setting goals, it is important to look to new irreversible impacts and the steady state circumstances. The end of the century is too soon to show that before but inevitable response especially for sea level rises.” Pearson added that: “What keeps cryosphere scientists up at night are irreversible thresholds, particularly West Antarctica and Greenland. The consensus figure for the irreversible melting of Greenland is at 1.6 °C.”

So what did we learn about the climate system in 2017? Here’s three that stand out, that should send shivers down the spines of policy makers. 

1.  2017 was the second hottest year on record and the hottest non-El Nino year on record

Whilst not all sources have yet released data on annual warming for last year, the Copernicus Climate Change Service, the first major international weather agency to report global 2017 temperatures, said they averaged 1.2 °C above pre-industrial times. 2017 was slightly cooler than the warmest year on record, 2016, and warmer than the previous second warmest year, 2015, Reuters reported.

Other organisations have unofficial figures which either agree with this assessment, or say that 2017 has tied with 2015. And last year was Australia's third-warmest year on record.

It is no surprise that the last three years have been the hottest on the instrumental record. What is remarkable is that 2017 was as hot, or hotter than 2015, because 2015 and 2016 were both El Nino years, and the evidence shows that El Nino years are, on average, about 0.15 °C warmer than La Nina years.In fact, a remarkably hot 2017 crushed the old record for hottest non-El Niño year (2014) by an astounding 0.17 °C.

The underlying temperature trend is being driven by continuing high levels of climate pollution: The UN says carbon dioxide levels grew at record pace in 2016. The atmospheric carbon dioxide  averaged 403.3 parts per million (ppm) over the year, up from 400 ppm in 2015. The growth rate was 50% faster than the average over the past decade.

And global carbon emissions are headed up again after three years in which human-caused emissions appeared to be leveling off. A 2% increase is projected overall, with the highest rise coming in China, according to new research presented at the climate talks in Bonn.

In 2017, we also learned that there was no pause in global warming: the so-called ’slow down' in climate change between 1998 and 2012 was caused by a lack of data from the Arctic.

2. It is likely to get hotter than we think

Two significant pieces of work released towards the end of 2017 suggest that warming is likely to be greater than the projections of the Intergovernmental Panel on Climate Change (IPCC), on which climate policy-making and carbon budgets are generally based. 

This is because what is called Equilibrium Climate Sensitivity (ECS), an estimate of how much the planet will warm for a doubling in the level of greenhouse gases, is higher than the median of the IPCC’s modelling analysis. 

In “Greater future global warming inferred from Earth’s recent energy budget” published in Nature in December 2017, Brown and Caldeira compared the performance of a wide range of climate models (raw model projections) with recent observations (especially on the balance of incoming and outgoing top-of-the-atmosphere radiation that ultimately determines the Earth’s temperature), in order to assess which models perform best.

The models that best capture current conditions (the “observationally-informed” models) produce 15% more warming by 2100 than the IPCC suggests, hence reducing the “carbon budget” by around 15% for the 2C target.

 For example, they find the warming associated by the IPCC with RCP 4.5 emissions scenario would in fact “follow the trajectory previously associated with (higher emissions) RCP 6.0” scenario. 

They also find that the observationally-informed ECS prediction has a mean value of 3.7 °C (for a doubling of the atmospheric greenhouse gas level), compared to 3.1 °C used in raw models, and in the carbon budget analyses widely used by the IPCC, the UN and at climate policy conferences.

In “Well below 2C: Mitigation strategies for avoiding dangerous to catastrophic climate changes,” published in September 2017, Xu and Ramanathan look at what are called the “fat tail” risks. These are the low-probability, high-impact (LPHI) consequences (“fat tails”) of future emission scenarios; that is, events with a 5% probability at the top end of the range of possible outcomes. 

These “top end” risks are more likely to occur than we think, so “it is important to use high-end climate sensitivity because some studies have suggested that 3D climate models have underestimated three major positive climate feedbacks: positive ice albedo feedback from the retreat of Arctic sea ice, positive cloud albedo feedback from retreating storm track clouds in mid-latitudes, and positive albedo feedback by the mixed-phase (water and ice) clouds.” 

When these are taken into account, the researchers find that the ECS is more than 40% higher than the IPCC mid-figure, at 4.5-4.7 °C. And this is without taking into account carbon cycle feedbacks (such as melting permafrost and the declining efficiency of forests carbon sinks), and increase methane emissions from wetlands, which together could add another 1 °C to warming be 2100. 

This work complements other recent work which also suggests a higher climate sensitivity:

• Fasullo and Trenberth found that the climate models that most accurately capture observed relative humidity in the tropics and subtropics and associated clouds were among those with a higher sensitivity of around 4 °C.

• Zhai et al. found that seven models that are consistent with the observed seasonal variation of low-altitude marine clouds yield an ensemble-mean sensitivity of 3.9 °C. 

• Friedrich et al. show that climate models may be underestimating climate sensitivity because it is not uniform across different circumstances, but in fact higher in warmer, inter-glacial periods (such as the present) and lower in colder, glacial periods. Based on a study of glacial cycles and temperatures over the last 800,000 years, the authors conclude that in warmer periods climate sensitivity averages around 4.88 °C. Professor Michael Mann, of Penn State University, says the paper appears "sound and the conclusions quite defensible."

• Lauer et al. found that climate models that most accurately simulate recent cloud cover changes in the east Pacific point to an amplifying effect on global warming and thus a more sensitive climate. 

And the bottom line?  If this work is correct, then the pledges made under the Paris Accord would not produce warming of around 3 °C as is widely discussed, but a figure closer to and even above 4 °C. And the total carbon budget would a quarter smaller than is generally accepted, or even less.

3. Climate models under-estimate future risks

This year, the Breakthrough Centre for Climate Restoration in Melbourne, published What Lies Beneath, on the scientific understatement of climate risks. The report found that human-induced climate change is an existential risk to human civilization, yet much climate research understates climate risks and provides conservative projections. Reports from the Intergovernmental Panel on Climate Change that are crucial to climate policymaking and informing public narrative are characterized by scientific reticence, paying limited attention to lower-probability, high-risk events that are becoming increasingly likely. (Disclosure: I was a co-author of this report.) 

But don’t take my word.  At the climate policy conference in Bonn, Phil Duffy, the Director of the Woods Hole Institute, explained the scientific reticence regarding the biggest system feedback issues:

"The best example of reticence is permafrost…  It’s absolutely essential that this feedback loop not get going seriously, if it does there is simply no way to control it… The scientific failure comes in because none of this is in climate models and none of this is considered in the climate policy discussion… climate models simply omit emissions from the warming permafrost, but we know that is the wrong answer because that tacitly assumes that these emissions are zero and we know that’s not right…"

And the problems of underestimation of future climate impacts from current models was explicitly recognized by the US government in its Climate Science Special Report: Fourth National Climate Assessment. In a chapter on “Potential Surprises: Compound Extremes and Tipping Element,” two key findings were:

Positive feedbacks (self-reinforcing cycles) within the climate system have the potential to accelerate human-induced climate change and even shift the Earth’s climate system, in part or in whole, into new states that are very different from those experienced in the recent past (for example, ones with greatly diminished ice sheets or different large-scale patterns of atmosphere or ocean circulation). Some feedbacks and potential state shifts can be modeled and quantified; others can be modeled or identified but not quantified; and some are probably still unknown. (Very high confidence in the potential for state shifts and in the incompleteness of knowledge about feedbacks and potential state shifts).

• While climate models incorporate important climate processes that can be well quantified, they do not include all of the processes that can contribute to feedbacks, compound extreme events, and abrupt and/or irreversible changes. For this reason, future changes outside the range projected by climate models cannot be ruled out (very high confidence). Moreover, the systematic tendency of climate models to underestimate temperature change during warm paleoclimates suggests that climate models are more likely to underestimate than to overestimate the amount of long-term future change (medium confidence).

• The problem is that the notion that future climate changes may be faster and hotter than those projected by climate models is one rarely understood by climate policy-makers, and rarely discussed by those who do understand.

If climate policymaking is to be soundly based, a re-framing of scientific research within an existential risk-management framework is now urgently required. This must be taken up not just in the work of the IPCC, but also in the UN Framework Convention on Climate Change negotiations if we are to address the real climate challenge.

http://www.climatecodered.org/2018/01/what-we-learned-about-climate-system-in.html

Millennial Scale Change From Lake El’gygytgyn, NE Russia: Did We Step Or Leap Out Of The Warm Pliocene Into The Pleistocene?

43rd International Arctic Workshop, Amherst, Mass., March 11-13, 2014

Julie Brigham-Grette¹, Martin Melles², Pavel Minyuk³, and the El'gygytgyn Science Team⁴

¹University of Massachusetts, Amherst
²University of Cologne
³NEISRI-RAS Magadan
⁴USA, Germany, Russia

The Pliocene-Pleistocene climate evolution of the Arctic must have modulated the glacial history of Greenland and the onset of Northern Hemisphere glaciation. What is known from the terrestrial stratigraphy of Arctic climate change comes from sites that are spatially and temporally fragmented. In 2009, International Continental Deep Drilling at Lake El’gygytgyn (67^o 30' N, 172^o 05' E) recovered lacustrine sediments dating back to 3.58 Ma that provide the first time-continuous Pliocene-Pleistocene Arctic paleoclimate record of alternating glacial-interglacial change. The warmest/wettest Pliocene interval of the lake record occurs from ~3.58-3.34 Ma and is dominated by exceptional tree pollen implying July temperatures nearly 7-8 ^oC warmer than today, with nearly ~3 times the annual precipitation. Atmospheric CO2 levels are estimated to have been 360-400 ppm implying exceptionally high climate sensitivity and polar amplification. In fact, pollen spectra and modern analog analysis show an unbroken persistence of summers much warmer and wetter than the last interglacial, MIS 5e until nearly 2.2 Ma. Extreme warmth in the Mid Pliocene Arctic occurs at the same time ANDRILL results suggest the West Antarctic Ice Sheet was non-existent.

Using physical, chemical, and biological proxies we find pronounced glacial episodes commenced ~2.6 Ma ago, but the full range of typical Pleistocene glacial/interglacial change was not established until ~1.8 Ma ago. Greenland must have also responded to numerous “super interglacials” during the Quaternary record, with maximum summer temperatures and annual precipitation, especially during MIS 9, 11 and 31, at Lake El’gygytgyn exceeding that documented for MIS 5e. The correspondence of many of these super-interglacials with retreat of the West Antarctic Ice Sheet (Naish et al. 2009) could coincide with intervals when the Greenland Ice was reduced in size. The climate record from Lake El’gygytgyn, especially the history of past interglacials, provides a fresh means of testing the evolving magnitude of polar amplification over time, and the sensitivity of the Greenland Ice Sheet to extreme warmth in the rest of the Arctic.

Brigham-Grette, J., Melles, M., Minyuk, P., Andreev, A., Tarasov, P., DeConto, R., Koenig, S., Nowaczyk, N., Wennrich, V., Rosén, P., Haltia-Hovi, E., Cook, T., Gebhardt, T., Meyer-Jacob, C., Snyder, J., Herzschuh, U.  Pliocene warmth, extreme polar amplification, and stepped Pleistocene cooling recorded in NE Russia. Submitted to Science, 21 November 2012; in revision March 2013.

Melles, M., Brigham-Grette, J., Minyuk, P., and others. 2012. 2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia. Science, 337, 315-320.

Naish, T. et al., 2009. Obliquity-paced Pliocene West Antarctic ice sheet oscillations. Nature, 458, 322-328.

See also Climate of the Past, special issue on Lake El’gygytgyn, 20+ manuscripts.

http://instaar.colorado.edu/meetings/AW2013/abstract_details.php?abstract_id=78

John Abraham: Climate change and sensitivity: not all Watts are equal

A new paper by Drew Shindell of NASA provides more evidence to support relatively high climate sensitivity estimates

by John Abraham, "Climate Consensus - The 97%," The Guardian, March 11, 2014

Air pollution in cities like Beijing tends to be located in the northern hemisphere and has a big impact on global temperatures. Photograph: Ed Jones/Photograph: Ed Jones/AFP/Getty

We hear a lot of talk these days about climate sensitivity. It is often considered the most important measure for predicting how much the Earth's temperature will increase as we emit heat-trapping gases like carbon dioxide. 

But, the term sensitivity has to be used carefully because it can mean different things in different contexts. For instance, there is a long-term (equilibrium) sensitivity to doubling carbon dioxide which refers to the ultimate temperature reached by the planet if we were to double carbon dioxide. There are also shorter term (transient) sensitivities which relate to temperature changes as heat trapping gases increase at some specified rate.

Values for climate sensitivity in general can be obtained many ways. My favorite way is by looking at deep history. If we can measure how sensitive the climate was in the past, perhaps we can infer its sensitivity now. A second way is through the use of modern temperature records and recent greenhouse gas levels. A third way is through the use of climate models (computer programs that replicate the Earth climate system). Regardless of the method used, there is general agreement that if we were to double carbon dioxide, the Earth's surface temperature would eventually increase by 1.5–4.5°C (2.7–8.1°F). Obviously, if the Earth sensitivity is at the upper end of the range, we are in trouble.

Recently, there have been some studies which suggest that maybe the climate sensitivity is at the lower end of this range. Most of these studies have only used the second method to calculate sensitivity, a fact that will soon become important. In addition to real science studies, there have been policy organizations that have promoted these low-sensitivity results. But my question is, what does the science say? Fortunately, a paper just published in Nature Climate Change provides some guidance on this question. The study was completed by Dr. Drew Shindell from NASA, and what he found was exciting. It turns out, not all Watts are equal. Energy changes to the Earth system from changes of sun-reflecting particulates or from ozone have a different impact than energy changes from carbon dioxide.

 Dr. Drew Shindell, Climate scientist at NASA.

The Earth has a greater sensitivity to particulates and ozone than to carbon. The reason for this seemingly strange behavior is that aerosols are largely located near industrialized areas in the Northern Hemisphere. This hemisphere also happens to contain much more land area than the south – and land regions are more sensitive to changes in energy, at least in the near term. In short, particulates and ozone impact more sensitive parts of the planet. Carbon dioxide, on the other hand, spreads out uniformly across the globe – it doesn't accumulate in one hemisphere or another.

However, let's not get too excited about particulates saving us from global warming. Dr. Shindell also showed that while in the short run, the cooling effect from particulates matters a lot, in the long run, it doesn't make much of a difference. The impact can be seen in this figure which shows the prior expectations of the climate (dashed line) alongside the revised prediction (solid). By 2050, there really is little difference.

 Temperature responses for uniform heating (dashed) and new non-uniform heating (solid).

What does this have to do with climate sensitivity? Well, it means that studies based on observed warming (such as the recent low climate sensitivity studies) have underestimated the sensitivity because they did not account for the greater response to aerosol forcing. Multiple lines of evidence are now consistent showing that the climate sensitivity is very unlikely to be at the low end of the range. The consequences of climate change are thus likely to be towards the more damaging end of the estimates, unless we take action to quickly reduce our emissions.

As Dr. Shindell aptly states,

"I wish we could take some solace from the slowdown in the rate of warming, but all the evidence now agrees that future warming is likely to be towards the high end of our estimates so it's more clear than ever that we need large, rapid emissions reductions to avoid the worst damages from climate change."

Fortunately for us, the technologies are available for us to reduce emissions, we just need the will.

http://www.theguardian.com/environment/climate-consensus-97-per-cent/2014/mar/11/climate-change-sensitivity-shindell

Climate scientist to US Senate: 'Climate change is a clear and present danger'

In a Senate hearing on President Obama's Climate Action Plan, Dessler summarised the science behind the climate threat

by Dana Nuccitelli, "Climate Consensus - The 97%," The Guardian, January 20, 2014

Andrew Dessler warned the US Senate about climate impacts like increased precipitation and floods. Photograph: Christopher Lee/Getty Images

 

Last Thursday, the US Senate Committee on Environment & Public Works held a 4-hour hearing to review President Obama's Climate Action Plan. The hearing began with statements from the committee members, and then proceeded with two expert panels. The first was comprised of administrators of government agencies that are key to implementing President Obama's Climate Action Plan, like EPA administrator Gina McCarthy. The second panel was comprised of climate science and policy experts.

Andrew Dessler, a climate scientist from Texas A&M University, was one of the expert climate science witnesses invited to testify. In his testimony, Dessler simply and clearly articulated what we know about climate change, and why he personally views it as "a clear and present danger." Dessler's main points were:

1. The climate is warming - not just the atmosphere, but also the oceans, which are rising as a result, and ice is melting.

2. Most of the recent warming is extremely likely due to emissions of carbon dioxide and other greenhouse gases by human activities. This is supported by overwhelming evidence and hence was a conclusion of the 2014 IPCC report.

3. Future warming could be large. Over the 21st century, if we continue with business-as-usual, the IPCC projects 2.6–4.8 °C average global surface warming.

4. The impacts of this are profound. The virtually certain impacts include increasing temperatures, more frequent extreme heat events, changes in the distribution of rainfall, rising seas, and the oceans becoming more acidic. There are numerous additional possible impacts as well.

Strangely, in her testimony, Georgia Tech climate scientist Judith Curry directly contradicted Dessler's second point, arguing that the 2014 IPCC report actually weakens scientists' confidence in human-caused global warming. Curry's evidence to support that assertion boiled down to arguing of a supposed 'lack of warming since 1998,' discrepancies between models and observations during that time, a lower climate sensitivity range in the 2014 than the 2007 IPCC report, and the fact that Antarctic sea ice extent has increased.

However, Dessler was correct that the IPCC increased its confidence in human-caused global warming between 2007 and 2014. It did so because the scientific evidence that humans are the dominant cause of global warming over the past century grew significantly stronger in recent years. 

 

Net human and natural percent contributions to the observed global surface warming over the past 50-65 years according to Tett et al. 2000 (T00, dark blue), Meehl et al. 2004 (M04, red), Stone et al. 2007 (S07, light green), Lean & Rind 2008 (LR08, purple), Huber & Knutti 2011 (HK11, light blue), Gillett et al. 2012 (G12, orange), Wigley & Santer 2012 (WS12, dark green), and Jones et al. 2013 (J13, pink). 

  This conclusion has also been supported by research published after the 2014 IPCC report, showing that the natural internal variability of the climate can't account for recent global warming, and that the IPCC confidence in human-caused global warming is robust. And contrary to Curry's second point, the observed global warming has been consistent with the projections of the range of models used in the IPCC report.
 

IPCC AR5 Figure 1.4. Solid lines and squares represent measured average global surface temperature changes by NASA (blue), NOAA (yellow), and the UK Hadley Centre (green). The colored shading shows the projected range of surface warming in the IPCC First Assessment Report (FAR; yellow), Second (SAR; green), Third (TAR; blue), and Fourth (AR4; red). 

  In his testimony, Dessler also addressed the myth of the 'lack of warming.' In addition to being a result of cherry picking and largely an artifact of a lack of Arctic temperature station coverage, Dessler pointed to:

"...the continued accumulation of heat in the bulk of the ocean, which is a clear marker of continued warming. And because heat can be stored in places other than at the surface, a lack of surface warming for a decade tells you almost nothing about the underlying long-term warming trends ... I judge that there is virtually no merit to suggestions that the "hiatus" poses a serious challenge to the standard model [of human-caused global warming]."

Regarding the sensitivity of the climate to the increased greenhouse effect, Dessler pointed out that the 2014 IPCC report matched the 2001, 1995, and 1990 reports, estimating an eventual global surface warming of 1.5–4.5 °C in response to a doubling of atmospheric carbon dioxide. Only the 2007 IPCC report slightly changed the estimated range to 2–4.5 °C. Additionally, recent research has suggested that the true climate sensitivity lies on the high end of that range.

Regarding Antarctic sea ice, it's a complex issue, influenced by factors like ozone depletion and recovery and associated changes in wind patterns. However, the rapid loss of Arctic sea ice has been much larger than the small increase in Antarctic sea ice. Moreover, the Southern Ocean around Antarctica has warmed. Thus changes in Antarctic sea ice tell us very little about global warming.

Overall, Dessler was correct that the evidence for human-caused global warming is now stronger than ever. His testimony presented a compelling case for the threat of human-caused global warming, which he considers "a clear and present danger." Dessler and Curry agreed on one key point: that our actions can't alter the path of climate change over the next several decades (though Curry sounded like the Borg, calling emissions reductions efforts "futile"). It's true that we're locked in for significant additional global warming from the greenhouse gases we've already emitted.

However, Dessler pointed out that our actions today will determine whether we proceed on a dangerous path of continued rapid climate change over the second half of the 21st century, or stabilise global temperatures and minimize the threat posed by climate change. Dessler concluded:

"The scientific community has been working on understanding the climate system for nearly 200 years. In that time, a robust understanding of it has emerged. We know the climate is warming. We know that humans are now in the driver's seat of the climate system. We know that, over the next century, if nothing is done to rein in emissions, temperatures will likely increase enough to profoundly change the planet. I wish this weren't true, but it is what the science tells us."

http://www.theguardian.com/environment/climate-consensus-97-per-cent/2014/jan/20/climate-change-clear-and-present-danger

Climate Sensitivity Stunner: Last Time CO2 Levels Hit 400 Parts Per Million The Arctic Was 14 °F Warmer!

by Joe Romm, Climate Progress, May 12, 2013

We have pushed atmospheric CO2 levels to 400 parts per million (ppm) for the first time in human existence.

At the same time, a truly remarkably set of paleoclimate data shows the climate is much more sensitive to CO2 than we thought. And that means returning as quickly as possible back to 350 ppm is a vastly more rational course of action for a non-suicidal civilization, than, say continuing our unrestrained march toward 600 ppm, then 800, and then 1,000.

NOAA reported Friday that the daily mean concentration of CO2 in the air around Mauna Loa, Hawaii, surpassed 400 parts per million this week:

At the same time, a major new Science study of paleoclimate temperatures — based on “the longest sediment core ever collected on land in the Arctic” – revealed what happened the last time we had similar CO2 levels:

“One of our major findings is that the Arctic was very warm in the Pliocene [~5.3 to 2.6 million years ago] when others have suggested atmospheric CO2 was very much like levels we see today. This could tell us where we are going in the near future. In other words, the Earth system response to small changes in carbon dioxide is bigger than suggested by earlier models,” the authors state.

Yes, contrary to one or two (misreported) models suggesting a climate sensitivity on the low side, this study joins the myriad analyses of data that find it is likely to prove to be on the high side. For instance, recent observations of relative humidity in the tropics and subtropics found that “Future warming likely to be on high side of climate projections,” according to a November paper in Science.

How sensitive is the climate to increases in CO2, according to this “absolutely new knowledge” of paleoclimate temperatures?

Another significant finding to emerge from this first continuous, high-resolution record of the Middle Pliocene is documentation of sustained warmth with summer temperatures of about 59–61 

°F [15–16 °C], about 8 °C [14 °F] warmer than today.

This period of Arctic warmth “coincides, in part, with a long interval of 1.2 million years when the West Antarctic Ice sheet did not exist.” Indeed, sea levels during the mid-Pliocine were about 25 m [82 feet] higher than today!

It is worth noting that a 2009 analysis in Science found that when CO2 levels were this high 15–20 million years ago, it was 5–10 °F warmer globally and seas were also 75–120 feet higher.

The risks of failing to sharply curtail carbon pollution are enormous if the climate sensitivity is on the low side (see “Memo To Media: ‘Climate Sensitivity’ Is NOT The Same As Projected Future Warming, World Faces 10 °F Rise”). But the risks of inaction are beyond incalculable if climate sensitivity is in the middle end of the range, let alone the high end suggested by the paleoclimate data:

Science (1/11) study — On our current emissions path, CO2 levels in 2100 will hit levels last seen when the Earth was 29 °F (16 °C) hotter: Paleoclimate data suggests CO2 “may have at least twice the effect on global temperatures than currently projected by computer models.”

As I explained in Nature online back in 2008 (here), once you factor in carbon-cycle feedbacks, even the uber-cautious Fourth Assessment report (AR4) of the IPCC makes clear we are headed toward 1,000 ppm (the A1FI scenario). That conclusion has been supported by just about every major independent analysis, including a recent report by PricewaterhouseCoopers (see Study: We’re Headed To 11 °F Warming And Even 7 °F Requires “Nearly Quadrupling The Current Rate Of Decarbonisation”).

This new paper is just the latest to suggest the Arctic will warm much faster than the models have suggested. For instance, back in 2006, scientists analyzed deep marine sediments to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” That Nature study (subs. req’d) found Arctic temperatures almost beyond imagination – above 23 °C (74 °F) – temperatures more than 18 °F warmer than climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.

Clearly our climate models don’t do a good job of explaining what’s happening in the Arctic right now:

Arctic sea ice is melting much, much faster than even the best climate models had projected (actual observations in red). The reason is most likely unmodeled amplifying feedbacks. The image (from Climate Crocks via Arctic Sea Ice Blog) comes from a 2007 GRL research paper by Stroeve et al.

And this underestimation of polar amplification in turn leads the authors of the new study — and many other scientists — to conclude that the climate’s overall sensitivity is on the high side. As the UK Guardian reports:

Prof Robert Spicer, at the Open University and not part of the new study, agreed: “This is another piece of evidence showing that climate models have a systematic problem with polar amplification,” i.e., the fact that global warming has its greatest effects at the poles. “This has enormous implications and suggests model are likely to underestimate the degree of future change.”

Given that the Arctic is already losing ice several decades faster than any major climate model had projected, we should expect that the permafrost — which contains twice as much carbon as the atmosphere currently does — will also go faster than the models suggest.

Indeed, a 2008 study by leading tundra experts found “Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss.” The study’s ominous conclusion:

We find that simulated western Arctic land warming trends during rapid sea ice loss are 3.5 times greater than secular 21st century climate-change trends. The accelerated warming signal penetrates up to ,km inland….

This in turn suggests that the extra warming from the released permafrost carbon will be on the high side (see “Carbon Feedback From Thawing Permafrost Will Likely Add 0.4–1.5 °F To Total Global Warming By 2100”).

Anyone betting on a low sensitivity of the climate to carbon is literally betting against history.

Finally, this new analysis of Arctic sediments is a very impressive piece of work whose conclusions are hard to dismiss:

“It shows a huge warming – unprecedented in human history,” said Prof Scott Elias, at Royal Holloway University of London, and not involved in the work. “It is a frightening experiment we are conducting with our climate.”

The sediments have been slowly settling in Lake El’gygytgyn since it was formed 3.6 million years ago, when a kilometre-wide meteorite blasted a crater 100 km north of the Arctic circle. Unlike most places so far north, the region was never eroded by glaciers, so a continuous record of the climate has lain undisturbed ever since. “It’s a phenomenal record,” said Prof Peter Sammonds, at University College London. “It is also an incredible achievement [the study's work], given the remoteness of the lake.” Sixteen shipping containers of equipment had to be hauled 90 km over snow by bulldozers from the nearest ice road, used by gold miners.

Previous research on land had revealed glimpses of the Arctic climate and ocean sediments had recorded the marine climate, but the disparate data are not consistent with one another. “Lake El’gygytgyn may be the only place in the world that has this incredible unbroken record of sediments going back millions of years,” said Elias. “When you have a very long record it is very different to argue with.”

If you want to learn more about this research, you can read the news release, the study itself (subs. req’d) or watch this video from the lead author, where you will also learn how to pronounce “El’gygytgyn”:

http://thinkprogress.org/climate/2013/05/12/1993531/climate-sensitivity-stunner-last-time-co2-levels-hit-400-parts-per-million-the-arctic-was-14f-warmer/