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How Many Do You Know?

Reporting on climate change is growing daily. The Washington Post just announced the addition of more than 20 new positions for coverage of climate and extreme weather, and NBC renamed its weather group the climate unit. The media tell us in graphic detail about the disastrous consequences of hurricanes, coastal storms, and extreme temperatures, often including what is known about the contribution of climate change. They offered daily reporting from the international climate meetings last December in Glasgow, Scotland, and regularly report key statistics such as whether temperature records were broken. All these subjects are newsworthy and contribute to our understanding of climate change. Yet there are some fundamental facts that only rarely form the basis for a news story, but which are critical to understanding (1) why climate change is such an existential threat and (2) why there are a limited set of actions remaining to avoid disaster. Five of those fundamental facts:

1. Greenhouse gas (GHG) concentrations in the atmosphere are greater than at any time in the past several million years, when the earth’s climate was dramatically different. The last time the atmospheric CO2 amounts were above the current level, 420 parts per million, was more than 3 million years ago. The world then was much hotter, and the oceans covered much more of the earth. The earth’s average temperature was 2°–3°C (3.6°–5.4°F) higher than during the pre-industrial era, and sea level was 15–25 meters (50–80 feet) higher than today — a change that would doom many island states, flood much of the U.S. coast, and create millions of climate migrants among many disastrous consequences.

2. Reducing carbon emissions will do little to slow warming for the next two or three decades. Twenty-five to 40% of the CO2 in the atmosphere will remain for 500 years or more, meaning reductions in emissions have a very gradual impact on atmospheric concentrations. It’s a lot like slowly letting water out of a very full bathtub while the tap continues to run — the water level declines only gradually, if at all. It will take two to three decades before reducing CO2 emissions has much impact on atmospheric concentrations and the rate of warming. This short-term challenge is made even more difficult because reducing coal combustion will also reduce release of sulfates, pollutants that fall out of the air in days but reflect solar radiation and thus provide some offsetting cooling.

3. Reducing methane (natural gas), HFCs (chemicals widely used in air conditioning), and black carbon (soot) is our best hope for reducing warming in the next two to three decades. These “super climate pollutants” are much more potent warming agents than CO2 but because of their much shorter atmospheric lifetimes can be reduced much faster. For historical reasons, climate models and most reporting on the issue compare greenhouse gases based on their expected contribution to warming over 100 years. On this basis, methane has about 21 times the impact of CO2, but when compared over 20 years its impact is more than 80 times as great. To limit warming to 1.5°C, the goal of the Paris Agreement, methane emissions from the energy sector need to fall by 75% by 2030. This short-term action is critical for avoiding dangerous feedbacks and tipping points — the next key fact.

4. Further warming the next decade and beyond risks irreversible, catastrophic feedbacks and tipping points. Only aggressive short-term action along the lines described above can avoid this danger. Scientists increasingly warn that the warming that has already occurred — with more now unavoidable in coming years — is producing positive feedbacks that accelerate warming. To cite one example: melting of the permafrost at high northern latitudes could release massive quantities of CO2 and methane. This accelerated warming is, in turn, raising fears that the world is approaching dangerous tipping points: dramatic changes in ocean ecology, the climate system, and other natural systems with potentially catastrophic consequences.

5. The risks/costs of inaction will be much greater than the costs of action. The economic transformation required to reduce GHG emissions and stay within the temperature limits agreed in Paris will be massive in scale and complex in execution; the World Economic Forum estimates the cost to be on the order of several trillion dollars more per year than is currently going to climate-friendly investments. Yet the costs and dislocations that would arise from a more disorderly transition would be far greater, and the financial losses from the impacts of more extreme weather events potentially incalculable. As a recent post of the World Economic Forum headlined, “Why doing nothing is the biggest corporate climate risk of all.” On the other hand, cleaner energy and more efficient buildings and industry will have substantial economic, environmental, and social benefits not included in most economic analyses such as a dramatic reduction in health care costs.

These five facts are all critical to understanding why the implications of climate change are so profound and action to address it so urgent. The same facts are sometimes relevant to newsworthy developments, e.g., the excellent New York Times reporting with supporting graphics explaining climate tipping points and Washington Post article focusing on the importance of reducing methane emissions. Fortunately, there are multiple sources for becoming educated about the fundamentals of climate change short of taking university courses. I’ll review some of these in my next blog.

Alan Miller is a former climate change officer in the International Finance Corporation (2003–13) and climate change team leader, Global Environment Facility (1997–2003)