Global warming and climate change are phenomena that still find their skeptics. For Dr. Benjamin Santer, an awarded climate researcher at Lawrence Livermore National Laboratory, the matter may not be beyond questioning and regular scientific evaluation, but it is beyond doubt.
The majority of Palo Altans - 17 years after the International Panel on Climate Change (of which Dr. Santer is part) pointed to a "discernible human influence on climate" - won't be surprised to hear it.
As such, Dr. Santer delivered succinct data last week at the Unitarian Universalist Church of Palo Alto in a presentation that answered how we know rather than what we do regarding global warming: "How do we as scientists study cause and effect relationships in the climate system? What are our tools of the trade? What are the computer model simulations that we use? What are the statistical methods that we use?"
The presentation began with the groundwork of statistical evidence regarding global warming in the past decades and beyond.
Since 1880, our planet has seen a rise of .75° Celsius in its surface temperature. Satellite observations beginning in 1979 also report a .5° Celsius rise in the Earth's lower atmosphere.
A slew of other figures - each verified by multiple data sets - similarly find a steady increase over the past 30 years. These include ocean heat content, sea-surface temperature, and the temperature over both oceans and land. Not unexpectedly, the extent of sea-ice and the collective mass of glaciers have decreased.
Dr. Santer went on to explain our reasons for believing these effects to be anthropogenic (caused by man).
One of the slides ion his presentation points out that "in computer models of the climate system, the observed warming cannot be explained by natural causes alone." Only those models accounting for both natural and human factors will follow a temperature over time curve congruent with that seen in reality. Those reflecting natural forces alone - without influence of human factors - share a less worrying picture.
The validity of this evidence is predicated on the accuracy of a few dozen computer models. One way to test it involves seeing how well they simulate known phenomena, such as the present weather or climate changes over the past 150 years.
Computer models failing this type of litmus test might not be weighed into projections of Earth's predicament at the end of the 21st century. Other projections, "more democratic than meritocratic" in Dr. Sander's words, might give each computer model an equal voice.
One model ventures into an interesting hypothetical situation: If greenhouse gas emissions were stayed at 1990 levels, we would still see a temperature rise - though a much less worrying one - by the year 2100?
In next year's IPCC report, Dr. Santer expects to introduce more variables to provide an even more accurate picture of projected figures for the rest of our century.
Computer models, if believed accurate, provide strong but only ancillary proof to climate change. More tangible is the fact that current amounts of atmospheric carbon dioxide - the main culprit among greenhouse gases - have not seen such heights in 800,000 years.
The method behind such a confident and far-reaching claim now belongs somewhat to common knowledge: "Before the period of direct instrumental measurements, people have very cleverly extracted air trapped in bubbles in glacial ice. It's a natural time machine. You can go back and make inferences back hundreds of thousands of years now, about changes in atmospheric composition over time."
"Most of this rapid increase in atmospheric levels of carbon dioxide over the last century and a half is due to us; it's caused by the burning of fossil fuels."