One of the most popular ‘theories’ currently being used by climate change skeptics, is that increased CO2 concentrations don’t cause temperatures to rise, but rather a rise in temperature causes CO2 concentrations to increase. They argue this means that humans can’t be responsible for the current warming trend, but this argument makes little sense when examined in detail.
The next time you hear your favourite global warming naysayer point out that carbon dioxide lags temperature by 800 years in the glacial record, don’t be surprised. That’s exactly how it must be.
There were no coal burning plants 21,000 years ago spewing carbon dioxide into the atmosphere.
In other words since we know that past changes climate were not caused by millions of people driving their SUVs to Walmart to get more milk, it is very likely that something other than increased CO2 emissions triggered past changes in climate.
What the fact that CO2 lags temperature in the past does suggest is that positive feedbacks exists in the climate systems. In other words the warmer it gets the more CO2 is released into the atmosphere by natural processes; this is in addition to to any CO2 that we release by burning fossil fuels.
The CO2 lag does not in any way mean that human emissions of CO2 are not responsible for the current warming trend.
That is, it doesn’t matter whether you put carbon dioxide in naturally or unnaturally, the fact remains that it is a greenhouse gas and traps outgoing longwave radiation.
What it does mean is that tackling climate change has much more urgency because small changes in climate (natural or otherwise) can trigger feedback systems that can greatly amplify this signal.
The last thing we need is natural systems working against our efforts to reduce atmospheric greenhouse gas concentrations.