A response to Jonathan Katz on climate change

Dan Cohn, Michael Yue, Jennifer Smith

Dear editor,

We take issue with a number of points raised by professor Jonathan Katz concerning global climate change. We base our statements on data and analysis from two compilations of climate science: the IPCC’s 2007 Fourth Assessment Report (AR4) and an update to this work, the Synthesis Report from this year’s Copenhagen Climate Change Conference (CCCC). Both are available online.

First, Professor Katz asserts that there is “no evidence” that global warming will lead to an increase in the frequency of droughts or tropical storms. The trend toward increased droughts, tropical storms and flooding events over the past several decades documented in AR4 is still recognized in CCCC; it is predicted that with a 1 degree Celsius rise in ocean temperature, the number of most destructive cyclones may double, while the frequency of cyclones of lower intensity will increase by smaller increments. Drying of agricultural areas, severe droughts and major flooding events are also predicted to increase. While Professor Katz may choose to dispute this evidence, there nonetheless is a body of data supporting the idea that extreme events have been occurring more frequently and will continue to do so in a warming climate.

Also, Professor Katz implies that storms are the opposite of droughts, so the idea that both are plausible effects of global warming is illogical. This is not the case; increased global temperatures are predicted to intensify the entire hydrologic cycle, increasing both evaporation (over land as well as water) and precipitation. This causes more intense rain in areas currently experiencing high rainfall, as well as increased drought severity in already dry areas (AR4, CCCC).

Professor Katz also brings up natural climate warming since the Little Ice Age. While natural processes have certainly caused very substantial past climatic variation, climate models built on natural processes alone (which can accurately reproduce reconstructed temperature variation from the last few centuries) cannot reproduce the warming of the last several decades. Only when anthropogenic effects are added to the models do they accurately portray the warming we are experiencing (AR4).

Additionally, the assertion that there will not be any climate refugees is particularly difficult to accept, as climate refugees already do exist (e.g., “Climate Refugees in Pacific Flee Rising Seas,” Washington Times, April 19). If extreme weather events increase and sea level rise continues as predicted, their numbers can only increase.

Furthermore, Professor Katz’s estimate of sea level rise assumes a constant increase in sea level; however, the rate of sea level rise is larger than it was in 1993 and is predicted to continue increasing, particularly if thresholds for destabilization of high-latitude ice sheets are reached, something that is looking increasingly probable (CCCC). Thus, sea level will most likely rise substantially faster than he suggests.

Finally, it is important to clarify that longer growing seasons are not expected worldwide, nor will they necessarily be beneficial. According to AR4, global food production is projected (with medium confidence) to rise for global temperature increases between 1 degree and 3 degrees Celsius but diminish with greater warming. Semi-arid and tropical regions, however, would see food production decrease for even small temperature increases (AR4). With the projected rise in food production needed to sustain a rapidly growing population, humanity simply cannot afford to gamble away the stability of established agricultural systems.

Climate change is one of the most pressing issues of our time, and we welcome its discussion on campus. We hope that the University community will take the initiative to become more informed.


Dan Cohn
Michael Yue
Jennifer Smith, associate professor of earth and planetary sciences

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