Our civilization is built on coastlines. Oceans were the first grocery stores, providing easy protein for early humans who learned to fish and gather shellfish and seaweed. Oceans were the first highways, enabling early exploration, commerce and migration. Oceans remain vital sources of food and trade, even as societies have grown and advanced. That's why three-fourths of the world's major cities are located on coasts.
But despite their many blessings, the Earth's oceans are becoming a curse. By burning fossil fuel, we have already begun to unleash the vast quantities of water locked up in glaciers as ice. That melt has already begun raising sea levels, which are, as revealed by our most recent research, preparing for an invasion of our coastal communities the likes of which modern humans have never encountered.
To say that we're not ready for this oceanic assault would be an understatement. Our international goal for limiting warming won't be enough to hold the waters back. Even if we meet the target goal of limiting global warming to 2 degrees Celsius, we will have already released enough CO2 to drive a dangerous amount of melting. Without concerted efforts to tackle climate change, we are condemning our biggest, most prosperous and populated cities to an underwater existence.
We are, in effect, creating a world where there won't be just one Atlantis, but many. A world where thriving cities are invaded not by barbarians or battalions, but by the same waters that first facilitated their growth.
In the ancient past, long before the rise of humanity, the wobble of Earth's axis changed the amount of sunlight on polar regions, causing dramatic temperature changes over thousands of years. Using those episodes as reference points to how the oceans and ice sheets react to temperature changes, we are able to project what will happen as humanity continues polluting the atmosphere with fossil fuel's carbon dioxide waste.
What lies in store — according to the science — is startling. Sea levels are poised to rise as much as several meters in just 50 to 90 years. This means that billions of people currently living alongside the coast will likely be forced inland to new areas, triggering massive immigration problems (not to mention the infrastructure complications and economic costs of abandoning or adapting our most prosperous cities).
Our study — based on current observations, paleoclimate records and modeling — shows that the current framework of a 2-degree target as a "guardrail" of safety is misguided. We're publishing this study now, for discussion purposes and prior to a complete peer review, because the findings require greater awareness and understanding as the world works toward an international climate agreement in Paris this December.
To protect our coastal communities, we need to protect our climate. Protecting our climate means cutting out fossil fuels and focusing on clean energy. With a revenue-neutral price on carbon we can quickly stimulate exactly the sort of switch that's necessary to slow the ocean's rise, instead of allowing it to take over our coastal cities.
If this threat were from a foreign nation our response would be unequivocal, immediate and forceful. But because the enemy is us, we have dragged our feet for decades and resisted the necessary changes. Paralyzed by fears propagated by industrial interests, we remain unwilling to change the energy infrastructure that's fueling this problem. By putting a price on carbon and returning that revenue to the people, we can begin to turn back the rising tide that threatens to engulf our coastal communities.
Otherwise, Los Angeles, New York, Miami and three-quarters of the biggest cities on the planet should prepare for life underwater. With temperatures rising and ice melting, time is dwindling to save our cities. So let's get started — or else Atlantis awaits.
James Hansen is an adjunct professor at Columbia University Earth Institute and former director of the NASA Goddard Institute for Space Studies.