Proof for what? That climate changes? I already believe that. 800 years ago there was a megadrought that deprived lakes of so much water that they had entire forests growing on the exposed land. Since the rain returned, those lakes have re-filled, and the trees are well preserved in their oxygen free depths.
There have been ice ages and all sorts of changes in the climate. The Medieval Warm Period, the Little Ice age. There was a time when Vikings lived in Greenland, because there was less ice.
What I need proof for is that current change is being caused by anthropogenic CO2, and that the consequences will be catastrophic. I need evidence that the bad consequences of anthropogenic climate change will outweigh the good we get from burning fossil fuels, as well as the benefits of a warmer Earth with more CO2 for plants to thrive.
In the climate change debate, people often forget that under all but the most catastrophic scenarios, the future generations who will benefit from our current mitigation efforts will be much richer than we are. For example, Nigel Lawson points out that even under one of the worst case scenarios studied by the IPCC, failure to act would simply mean that people in the developing world would be “only” 8.5 times as wealthy a century from now, compared to 9.5 times as wealthy if there were no climate change.
Although it is probably true that the “best evidence” suggests a connection between human activities and a warming globe, this fact about the natural world does not automatically justify aggressive government interventions into the economy. Given the historical corruption of governments and the demonstrated resilience of free entrepreneurs, proponents of such measures have a much harder case to make.
EDIT: I am also being told, in the comments, that the climate change we are experiencing now is unprecedented, that we are causing a temperature rise at a rate that has never happened before, except in catastrophes. I need to see evidence for this. I am shown graphs of thermometer readings, usually with a lot of processing to combine readings from a large number of weather stations. This data is on the scale of several decades, maybe a couple centuries going back to at most the late 1800’s, showing a strong upward trend. Problems and accusations of cooking the data to create the desired conclusion aside, these are thermometer readings. They are then compared to proxies like ice core data and tree rings. Not only are these incompatible data sources, they are put on entirely different scales. Many thousands of years are compressed into the same space on the page as a hundred years on the thermometer readings graph.
Worst yet, the thermometer readings are combined on the same graph, as if they are the dame data source, to create the infamous “Hockey Stick” graph.
If the proxy data was valid and accurate, then it should be good up until today. Ice still forms, and trees still grow. Why combine it with thermometer readings, which may be giving us temperatures in entirely different locations.
But the most important thing is the scale. We need to be able to see that there has never been warming as fast as we see now. Show us what the proxies say about the last 100 years, and what they say about the last hundred thousand. Put them on an interactive computer graph, available on the internet, so anyone can scan it, adjust the scale, and see how fast temperatures were changing over any 100 year period.
If I can scroll through such a graph, and not find proxy data for a temperature change as fast as we are seeing now, I will be convinced that human activity is changing the climate.
SHOW ME THE DATA!