Richard Somerville is Distinguished Professor Emeritus and Research Professor at Scripps Institution of Oceanography at UC San Diego as well as the author of “The Forgiving Air” and a coordinating lead author of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. The CMMAP publication Climate Sense published his commentary “Concerns of a Climate Scientist” Aug. 2 and is republished below with permission.


Richard C. J. Somerville

Published on August 2, 2013

Scripps Institution of Oceanography University of California, San Diego

President Obama’s speech on June 25, 2013 proposed a broad array of new Federal initiatives to reduce the threat of severe climate change. This is encouraging news indeed, because until now, there has been little evidence in Washington of political leadership on this important issue. President Obama’s announced commitment to act has now given the world reasons for being more hopeful. In the months and years ahead, we shall see whether effective policies can be implemented that produce meaningful results.

What concerns me most about climate change now is the stark contrast between the apathy of the public and the troubling facts that we climate scientists have established and that President Obama clearly recognizes. Most people are not well informed about what our science has discovered. In the United States, we also have the sad spectacle that almost the entire national leadership of the Republican party still does not accept the most basic findings of mainstream climate science. In the 2012 US Presidential election, the topic of climate change was essentially ignored by both sides. Problems cannot be solved by pretending they do not exist, and future generations will not judge us kindly unless we accept the science and act quickly.

The existential threat of climate change affects national security, economic prosperity, and the health and safety of people throughout the world. It should not be marginalized as a niche issue of interest only to a few people whom we label as “environmentalists.” Journalists should never make the mistake of framing the issue as a controversy – is man-made climate change real and serious or not – in which both sides deserve equal time.

The plain fact is that what mankind decides to do in the coming years and decades will largely determine the climate that our children and grandchildren will inherit. To meet the very real threat of climate change caused by human activities, policymakers must listen to the science and then must act. Humanity needs to decide collectively how much man-made climate change is acceptable. Science cannot specify what level of climate change is “dangerous.” That is a question involving risk tolerance, values, priorities and other subjective concerns. It is governments that will decide, by their actions or inactions.

Governments already have made a tentative decision. Many governments have adopted the aspirational goal of limiting global warming to 2 degrees Celsius (or 3.6 degrees Fahrenheit) above the average pre-industrial temperatures of the 1800s. Given that goal, climate science can provide useful information about what actions are needed to give a reasonable chance of meeting the goal. Science tells us that it is urgent to act soon. The world has already warmed by almost half of the 3.6 degrees Fahrenheit goal. Some further warming is unavoidable. However, humanity has the ability to limit the amount of future climate change.

We are already watching human-caused climate change occur. It is not only a problem for the future. It is happening here and now. The warming is just a symptom. Climate is complex, and warming has many consequences. Melting Arctic sea ice and rising sea level are consequences. Extreme weather events today occur in a changed environment. For example, Hurricane Sandy, which killed hundreds of people and caused some 75 billion dollars in property damage in 2012, occurred in a climate with higher ocean temperatures and more water vapor in the air than only a few decades ago. The heat-trapping gases and particles that humanity has emitted into the atmosphere increase the odds of severe weather events, just as steroids taken by a baseball player can increase the odds of home runs. Today we are seeing climate change on steroids. To limit global warming to moderate or tolerable amounts, the entire world must act quickly to reduce these emissions. As the world’s only superpower, the United States needs to reduce its own emissions and must also provide leadership so that other countries will reduce their emissions too.

Carbon dioxide (CO2) is the single most important heat-trapping gas that humanity emits into the atmosphere. Because some of the CO2 that we emit will stay in the atmosphere for many centuries, it is our cumulative emissions that matter. If today’s rates of emitting heat-trapping gases and particles continue without change, then after just 20 more years the world will probably be unable to limit warming to 2 degrees Celsius.

To have a reasonable chance of meeting this 2 degree Celsius goal, the science shows that global emissions of heat-trapping gases and particles must peak soon and then start to decline rapidly, not in 50 or 100 years, but within the next 5 to 10 years, reaching near zero well within this century. Given the 2 degree Celsius goal already agreed to by many governments, the case for great urgency in taking meaningful actions to reduce emissions is a consequence of science. It is based on facts and evidence. It is not an ideological or political choice. We have a window of time within which we simply must act if we are serious about meeting the 2 degree Celsius goal. The window is still open, but it will soon close and will then remain closed.

If the world continues to procrastinate throughout the current decade, so that global emissions of heat-trapping gases and particles continue unabated for another ten years, then we will almost certainly have lost the opportunity to limit warming to 2 degrees Celsius. Thus, it is encouraging that President Obama’s announcement comes now, rather than later. All of us can help, and we climate scientists in particular can participate in the critically important effort to increase our knowledge of climate change and to communicate our understanding clearly and objectively to as broad an audience as possible.

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