Previous attempts to reconstruct global temperatures have only gone back a little over 1,500 years (illustrated by the gray areas on the chart above). The study could not go further back because it relied on a study of tree rings to study the climate change. It showed that global temperatures have risen very sharply in the last few decades. This was good evidence of global warming, but it was attacked by global warming deniers who said that the Earth had warmed before and this was a natural occurrence (not due to human over-consumption of fossil fuels).But there is now a new study that was done on global temperatures in the past. Because it relies on studies of fossilized ocean shells (instead of tree rings), this study is able to document global temperatures for the last 11,500 years (the purple line on the chart). And this is far enough back to include the last time the Earth experienced a warming trend. That period started about 11,000 years ago, and began cooling back down about 5,000 years ago. It took at least 4,000 years for that warming trend to reach its peak temperature (around 7,000 years ago).
This does show that the Earth has warmed in the past, but that was never in dispute. But while the Earth took at least 4,000 years to warm in the past, we are now exceeding those past temperatures -- and we have done it in only a few decades. If the current warming trend was caused by natural forces, we could expect it to take many thousands of years. The fact that we have risen that same amount in only a few decades is pretty conclusive proof that the current warming trend has been caused by humans (who are rapidly increasing greenhouse gases through massive burning of fossil fuels producing massive amounts of CO2).
That's pretty scary. But even scarier is the fact that we, so far, have done nothing to stem the tide of greenhouse gas production -- or taken any other action to slow the warming. There is no doubt that we will exceed the previous level of warming (which took thousands of years) by a significant margin -- and we will do that before the year 2050. Without dramatic action to stop this warming, it is unimaginable to think how high this warming could get to by the end of this century.
The evidence is in. There is significant global warming, and it is man-made. The time for debate is over. The time for action is here.
