The following is mostly from the book "A Brain for All Seasons" by William Calvin with additional things I have learned since reading the book.
Temperature is only part of climate change issue
Back in Darwin’s day there was an idea floated called gradualism. It basically said that the earth changed very slowly over a long period of time and that the earth had been basically like everyone experienced it for a very long period of time. This became the basis for a lot of science and held sway until just the last 30 years. Modern science did come to understand that there had been significant changes in geologic time like plate tectonics but most everyone accepted that things like climate changed very slowly.
Starting in the 1950’s the idea that information about the past could be gained from ice cores got started and cores were drilled in Greenland. By the late 1960’s several had been drilled and analyzed. The efforts to create temperature and rainfall data from these first cores were not believed because the data showed too much and rapid variation to be real. By the early 1980’s there was a resurgence in interest in ice core data and better methods of analysis had been developed. Low and behold the original data suddenly appeared to be correct and a shift from gradualism in terms of natural climate variation was underway.
Temperature is a very useful marker because it is more universally gathered and it is easy to analyze. The first slide (slide 1) is the temperature data from the GRIP ice core of Greenland’s Summit. The interesting thing to note on this slide is that the 10 thousand years of human history that we have a lot of detail on all occurred in a period of temperature variation in Greenland that looks very stable compared to the longer term record including the previous warm period just before the last ice age. As you can see the temperature swings that occurred in the earlier time span make the swings in the last 10 thousand years seem minor.
This next slide (slide 2) shows just the last 15 thousand years of data and shows temperature and precipitation. What is interesting here is that this clearly shows that Greenland goes from cooler and dryer to warmer and wetter. This also shows the “Medieval Warm Period” which is when the Norse settled Greenland and grapes grew in England. Immediately following that is what is know in history as the “Little Ice Age” when the Norse died in Greenland, glaciers expanded in the Alps and Europe suffered food shortages. Pleases note that the level of change in Greenland that collates to these events in Europe seem insignificant to the longer term trend of change.
The next slide (slide 3) shows the correlation for events in Greenland with Trade Wind Strength off of South America. This looks at a particular event known as the Younger Dryas. Clearly this shows that the step change in Greenland that occurred very quickly, a few decades, is also reflected in the Trade winds. The worlds climate is an interconnected system and changes one place collate with changes else where. The worlds weather patters can shift from one mode to another quickly, decades, and have devastating effects on local growing conditions. Remember the Sahara desert has gone from habitual grass savannah to desert a number of times.
The take home message is that humans are at risk even without the potential effects of human induced changes in CO2. But how do recent changes in CO2 play into what we just looked at. The next slide (slide 4) shows how CO2, Methane and Temperature taken form ice core data correlate. Now it is not possible to say which causes which but it is clear that they move together so it is reasonable to assume that there are connections between them and that they reinforce or influence each other.
The next slide (slide 5) shows a longer term record from newer data and again show a tight correlation between temperature and CO2. The take home is that the recent changes in atmospheric CO2 as shown on this slide, which are greater than anything seen in the last 400,000 years are likely to push the world climate system into instability and trigger changes similar to historic swings in temperature, wind and rain patterns.
The ice core data show that the world’s weather system is prone to sudden, decades, step changes in behavior and compared to all of recorded history the level of change common in the long term record could wipe out great quantities of modern man.
Should we be concerned YES
Should we be working to get CO2 under control YES
Is it more than just temperature YES