Global Warming Gaining Momentum

The world’s largest general scientific society, the American Association for the Advancement of Science, has issued an uncharacteristically blunt call to action on climate change. The must-read new report by the AAAS’s Climate Science Panel, “What We Know” has several simple messages:

  • We are as certain that humans are responsible for most recent climate change as we are that cigarettes kill;
  • Climate scientists agree: climate change is happening here and now. Based on well-established evidence, about 97 percent of climate scientists have concluded that human-caused climate change is happening; and
  • The science linking human activities to climate change is analogous to the science linking smoking to lung and cardiovascular diseases. Physicians, cardiovascular scientists, public health experts and others all agree smoking causes cancer. And this consensus among the health community has convinced most Americans that the health risks from smoking are real.

A similar consensus now exists among climate scientists, a consensus that maintains that climate change is happening, and human activity is the cause.

What kind of change is already happening? Average global temperature has increased by about 1.4˚F over the last 100 years. Sea level is rising, and some types of extreme events — such as heat waves and heavy precipitation events -– are happening more frequently. Recent scientific findings indicate that climate change is likely responsible for the increase in the intensity of many of these events in recent years.

What is the danger of continued inaction? We are at risk of pushing our climate system toward abrupt, unpredictable, and potentially irreversible changes with highly damaging impacts. We can think of this as sudden climate brake and steering failure where the problem and its consequences are no longer something we can control. In climate terms, abrupt change means change occurring over periods as short as decades or even years.”

Why must we act now? The sooner we act, the lower the risk and cost. And there is much we can do. Waiting to take action will inevitably increase costs, escalate risk, and foreclose options to address the risk. The CO2 we produce accumulates in Earth’s atmosphere for decades, centuries, and longer. It is not like pollution from smog or wastes in our lakes and rivers, where levels respond quickly to the effects of targeted policies (but they often go hand-in-hand).

deforestation and climate change

When asked on the press call why the AAAS felt the need for providing the public and policymakers yet another climate report, Dr. James McCarthy, Harvard oceanography professor and former AAAS President, said “The public has been misinformed by a colossal disinformation campaign.”

Scientists must speak out strongly and often because the subject is too important to leave to the misinformers.

McCarthy also made a point I thought was key: The risk concept — the risk of inaction — this is something that really hasn’t been emphasized. And if you just think back 20 years or 10 years – what we imagined twenty years ago about loss of Arctic sea ice – it was not thought to be anything that would be of concern in this century.

Ten years later, roughly 2000, we knew that we were on a trajectory that couldn’t be anticipated. Ten years ago, during that same era, it was not thought that Greenland would be losing ice dramatically in the next few decades, but within a few years we realized that was wrong.

Too many climate reports fail to focus on the risk of inaction. Not this one.

“The issue in estimating the appropriate incentive is very much the risk,” he said. “In other words, the expected outcomes have been the dominant determinant of what those estimates have been in the past. And I’m not sure they’ve adequately taken into account the potential for things to be worse than expected. You really do have to think about worst-case scenarios when you are thinking about risk management. When it’s a risk management problem, thinking about worst-case scenarios is not alarmist — it’s just part of the job. And those worst-case scenarios are part of what drives the price.”

This is a key point, which has also been made by Harvard economist Martin Weitzman, who has explained that climate cost-benefit analyses are “unusually misleading,” warning his colleagues that “we may be deluding ourselves and others.”

In the case of climate change, the worst-case scenario is the end of modern civilization as we have come to know it, a post-2050 world that has a carrying capacity considerably below 9 billion people – and one that continues to decline decade after decade. And yet this “worst-case scenario” is all but certain to be achieved if we merely continue on our business as usual path of climate inaction for a few more decades. That is why we must pay any price or bear any burden to avoid the worst-case.

The report is a good antidote to those non-scientists who claim global warming does not make weather more extreme and more destructive: Global warming has changed the pattern of precipitation worldwide. Flooding in the northern half of the eastern U.S., Great Plains and over much of the Midwest has been increasing, especially over the last several decades. These regional flooding trends in the northeast and upper Midwest are linked to increases in extreme precipitation and are consistent with the global trends driven by climate change.

At the same time, areas such as the U.S. Southwest are witnessing more droughts, and these too are consistent with global climate change patterns projected by climate models as a consequence of rising CO2 levels.

Since 1950, heat waves worldwide have become longer and more frequent. One study indicates that the global area hit by extremely hot summertime temperatures has increased 50-fold, and the fingerprint of global warming has been firmly identified in these trends. In the U.S., new record high temperatures now regularly outnumber new record lows by a ratio of 2:1.

Climate change has amplified the threat of wildfires in many places. In the western U.S., both the area burned by wildfires as well as the length of the fire season have increased substantially in recent decades. Earlier spring snowmelt and higher spring and summer temperatures contribute to this change. Climate change has increased the threat of “mega-fires” –- large fires that burn proportionately greater areas. Warming has also led to wildfires present in some regions where they have been absent in recent history.

Kudos to the AAAS for this report. They join the US National Academy of Sciences and the U.K. Royal Society in producing a new, highly readable climate report, though the AAAS has done a better job of bluntly laying out the risks.

Bottom line: If a generally staid, consensus-oriented body like the AAAS is alarmed, then we all should be. As climatologist Lonnie Thompson explained back in 2010: Climatologists, like other scientists, tend to be a stolid group. We are not given to theatrical rantings about falling skies. Most of us are far more comfortable in our laboratories or gathering data in the field than we are giving interviews to journalists or speaking before Congressional committees. Why then are climatologists speaking out about the dangers of global warming? The answer is that virtually all of us are now convinced that global warming poses a clear and present danger to civilization.

climate change and deforestation

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