March 30, 2017
The biggest unknown about future climate is human behavior. Everything depends on what humanity does. Those of us who are alive today have our hands on the thermostat that controls the climate of our children and grandchildren. Carbon dioxide is the most serious of the heat-trapping gases that human activities emit into the atmosphere. A considerable portion of the carbon dioxide we emit can remain in the atmosphere for many centuries. It accumulates.
Deciding how much global warming is tolerable is a political decision. It depends on priorities, values, risk tolerance, economics, and so forth. That’s how we got the 2-degree Celsius target of the 2015 Paris Agreement. This target is an international commitment to take actions that will limit global warming to 2 degrees Celsius (3.6 degrees Fahrenheit) above the average pre-industrial temperature of the Earth. We’ve already experienced about half that much warming.
Now that the nations of the world have agreed in Paris on how much warming is to be allowed, climate science can tell us approximately how much more carbon dioxide and other heat-trapping gases and particles can be emitted. To have a reasonable chance of meeting the 2-degree Celsius target, the science shows clearly that emissions need to be reduced drastically and quickly. Science is based on facts and evidence. Politics sets the target, but the urgency of reducing emissions arises directly from the physics and chemistry of the climate system. It has nothing to do with politics.
In the United States today, many corporations and states and localities are taking strong actions to mitigate climate change, and they can continue to act, regardless of what the Trump administration does. Many other countries are acting vigorously too, and they will continue to act. Analysis shows that the cost of mitigating climate change is small compared with the costs of dealing with the damage that unmitigated climate change will cause. For example, doing nothing about climate change can lead to sea level rise so large that coastal cities must eventually be abandoned. Their populations will be forced to move to higher ground.
Yet President Donald Trump has nominated many people to his cabinet, and to other high positions in his administration, who simply do not accept the scientific consensus on climate change, namely that it is real, it is serious, it is happening here and now, and it is overwhelmingly human-caused. This consensus is exceptionally robust, supported by some 97 percent of climate scientists who are most active in publishing research. Trump may well be the only head of state of a major nation who denies the reality and seriousness of human-caused climate change. Will he choose to be an international laughingstock, mocked and scorned by other heads of state?
Polls show that most Americans would prefer to see strong federal government actions on climate change. Despite a Trump administration led by people who ignore facts and reject science, the forces driving clean energy will continue, regardless of any efforts by Trump to reverse them. The market is turning against fossil fuels. Coal companies are now going bankrupt. In many places, solar and wind energy without subsidies are already cheaper than fossil fuels. The energy source for wind and solar is free. Fossil fuel plants have commodity costs for the fuel they burn. Vehicle electrification is happening fast. Clean energy is destined to be a leading source of jobs and economic growth.
Prosperity does not require emitting heat-trapping gases. Everyone who takes climate change seriously should stay hopeful, remain active, and work hard to build on the progress already made. And be optimistic!
Distinguished Professor Emeritus and Research Professor
Scripps Institution of Oceanography, University of California, San Diego