Senate Committee on Environment and Public Works
State of the Science, Where are we now?
2 May 2001
John R. Christy, Verbal remarks
Thank you Mr. Chairman and Committee Members. I am pleased to be here to speak to you again about climate change. I am John Christy, Professor of Atmospheric Science and Director of the Earth System Science Center at the University of Alabama in Huntsville. I am also Alabama’s State Climatologist and recently served as one of the Lead Authors of the IPCC. I will refer to the figures at the back of your copies of my written testimony.
I want to say first that carbon dioxide, the agent thought to exert the largest part of human-related climate change, is literally the lifeblood of the planet. The green world we see around us would be gone without it. Carbon dioxide means life, and in concentrations several times its current value promoted the development of the plant world we now depend on and enjoy. Carbon dioxide is not a pollutant. Will CO2 increases affect climate significantly? Models suggest the answer is yes, though I have serious doubts.
A common feature of climate model projections with CO2 increases is a rise in the global temperature of the atmospheric layer from the surface to 30,000 feet. This temperature rise itself is projected to be significant at the surface, with similar or increasing magnitude as one rises through this layer called the troposphere.
Over the past 22-years various calculations of surface temperature indeed show a rise between +0.52 and +0.63 °F (0.29 and 0.35 °C). This is about half of the total rise observed since the 19th century. In the troposphere, however, various estimates which include the satellite data Dr. Roy Spencer of NASA and I produce, show only a very slight warming between +0.00 and +0.15 °F (+0.00 and +0.08 °C) – a rate less than a third that observed at the surface as pictured in Fig. 1. New evidence shown in Figs. 2 and 3 continues to reveal the remarkable consistency between independent measurements of this upper air temperature.
Since my last appearance before this committee, there has been one year above the 20-year average and two below it. And, rather than seeing a rise in the global temperature thatincreases with altitude as climate models project, we see that in the real world since 1979 the warming decreases substantially with altitude.
The reality of the past 22 years may only indicate that the climate experiences large natural variations in the vertical temperature structure which climate models have yet to reproduce. However, this means that any attention drawn to the surface temperature rise over the past 20+ years as evidence of climate change must also acknowledge the fact that the bulk of the atmosphere that was projected to warm significantly has not. One modeler told me recently that this surface versus troposphere difference was the largest problem they faced.
This vertical temperature variation is a curious and unexplained issue regarding global average temperatures. But we don’t live 30,000 feet in the atmosphere, and we don’t live in a global average. We live at the Earth’s surface in specific places. Making local and regional projections of surface climate are virtually impossible. An example from Alabama is useful here only to illustrate the difficulty of providing regional predictions with some confidence.
In Fig. 4 you will see several climate model runs which attempt to reproduce Alabama’s temperature from 1860 to the present, and then to predict its temperature out to 2100. These complex models incorporate solar changes, increasing CO2, aerosol cooling (a highly uncertain hypothesis) and so on. It is clear that the model runs did not do especially well over the time period of observations, with none predicting the actual cooling we have seen in Alabama over the last century. If in trying to reproduce the past we see such errors, one must assume that predicting the future of regional climate will produce similar errors.
I want to encourage the committee to be skeptical of media reports in which weather extremes are given as proof of human-induced climate change. Weather extremes occur somewhere all the time. For example, the U.S. temperature for last November and December combined was estimated to be the coldest since records began in 1895. That does not prove the U.S. or the globe is cooling or that climate is changing unnaturally. What it demonstrates is that extremes occur all the time.
Other climate data give similar non-alarmist results and therefore are overlooked by the media. Hurricanes have not increased. Thunderstorms, hail, and tornadoes have not increased. Droughts and wet spells have not statistically increased or decreased in the U.S. as shown in Fig. 5. Now, let me quickly add that today we have many more people and much more wealth in harm’s way so that losses have definitely risen, but that is not due to climate change.
When looking back over the past 2000 years in Fig. 6 we see that the most significant droughts in the Southwestern US, for example, occurred prior to 1600. We may well see one of those serious droughts again this century without any appeal to human causation.
Regional climate change, including that part that might be human related, is essentially impossible to predict at this point. This is an exceedingly more complex problem than predicting a simple global average temperature, which itself is not so accurately done as shown earlier.
I am decidedly an optimist about this situation. Our country is often criticized for producing 25% of the world’s anthropogenic CO2. However, we are rarely recognized and applauded for producing with that CO2 25% of what the world wants and needs; it’s food, technology, medical advances, defense, and so on. As Fig. 7 shows we in the U.S. will continue to produce more and more of what the world wants with increasing energy efficiency.
In summary I would say as someone who actually produces and studies climate information that I find pronouncements today about climate change catastrophes due to increased greenhouse gases to be overly alarmist.