For several years now, I've been writing in some detail about the science of climate change and the typically false climate denier arguments (md444444444) is propagating. A popular myth among climate skeptics is that historically atmospheric CO2 levels have risen after temperature increases started. Thus, it's temperature increases that cause CO2 increases and not vice-versa as basic climate science and physics would have us believe.
In a major breakthrough 2012 study, Shakun et al scientifically examined 80 ice core records from around the globe - many records extending back to the last glacial-interglacial transition which began 18,000 years ago - recording sea surface temperatures for the marine records and surface air temperatures. The atmospheric CO2 was compared to these many different temperature records to determine whether the CO2 increases led or lagged temperature changes in the various geographic locations and for the planet as a whole. The answer is YES - CO2 leads and lags.
Shakun et al proved that the fact that a temperature increase causes CO2 increase does not undermine fact that a CO2 increase causes temperature increase. Around 19,000 years ago, the Earth's orbital cycles triggered the initial warming in Greenland and Arctic regions.This caused fresh water to flood into the oceans ultimately causing a seesawing of heat between the Northern and Southern hemispheres. Then, around 18,000 years ago, the Southern Hemisphere oceans warmed first driven by the orbital cycles, subsequently releasing CO2 into the atmosphere around 17.500 years ago. This in turn caused the entire planet to warm by the increased greenhouse effect.
To summarize: although CO2 did** lag** behind a small orbital-caused temperature change mostly in the Southern Hemisphere, it led as the primary driver behind most of the glacial-interglacial warming. Shakun et al's research data revealed that approximately 7% of the glacial-interglacial global temperature increase happened before the CO2 rise, but approximately 93% of the global warming happened after the CO2 increase.
For six thousand years prior to the Industrial Revolution, slow cooling was the trend at an average rate of about 0.2C per millennium or 1,000 years. There were up and down variations due to changes in ocean currents and solar output. However, those changes did not exceed 0.1C per century. In dramatic contrast, the global temperature climb is now nearly 1.0C - with most of that increase occurring the last 40 years! And solar output has been down during that period. Given the increased warming during same period of relatively weak orbit forcing and solar activity and extremely long atmospheric lifetime of abnormally huge levels of anthropogenic carbon released llast 40-50 years, it's pretty clear no ice age is around the corner for at least thousands of years in the views of most scientists.
Just look at the northern ice sheets. If they were growing, the 10,000 year process of glaciation climate skeptics (e.g., md444444444) say is coming to planet Earth may actually have already begun. But, the scientific facts are that both hemispheres are warming up at a rapid rate primarily from AGW reinforced by multiple negative feedback systems. The Arctic region is warming up at much higher temperature levels than land temperatures. Arctic permafrost and sea ice are degrading and melting even faster. The vast amount of ice on land is the worst potential contributor to significant sea level rises. The planet's two largest ice sheets in Greenland and Antarctica are being deleted at an astonishing rate of 120 cubic miles each year. More disturbing, the rate of loss of ice from Greenland and Antarctica has more than doubled since 2009!
As oceans warm and acidify, their capacity to hold CO2 in dissolved form decreases, thus increasing the dispersal of CO2 into the atmosphere, making Earth ever warmer. The present CO2 atmospheric concentration of 400ppm and rising is the highest on record in 800,000 years. Normally, carbon naturally removed from the atmosphere over millions of years and stored in vast rock reserves would be released back into the atmosphere over millions of years. Human extraction and release of this material is now being done in very short periods of time.
Arguing about the science of AGW climate change, e.g., whether CO2 is a cause or an effect of global warming, is over.
It seems the IPCC in its recent meeting has finally stepped up to the reality we don't have much time. We are already committed to a multi-century climate change reality created by the cumulative past, present and future emissions - at least 40% of which stay in the atmosphere for up to 800 years. The task now is to quickly bring CO2 emissions down from a gigantic 40 billion tons/year today (including methane) to less than 15 billion tons by 2035, to less than 5 billion tons by 2050. We've got a long ways to go, but the goal of a full transition to green energy in all forms and ways is still possible by 2050. If this doesn't happen, an already guaranteed high 2C maximum temperature increase will surely become a disastrous 3-4C increase by 2050. For more background, (See: Parts 1-5: Conversion to Renewable Energy Is Going Too Slowly to Avoid Catastrophe by 2050, by F. Thomas and J. Lawrence).