For years the public wondered "Is global warming happening?" as the IPCC climate models predicted - instead the HadCRUT temperature dataset clearly shows global temps cooling off
(click on image to enlarge)
The simple answer from the empirical observations is 'No.'
The IPCC climate models, using the business-as-usual CO2 emissions scenario A1F1 predicted a best estimate of global temperature increase of +4.0 degrees by year 2100. That prediction was based on year 2000 being the starting point.
Thus, per the IPCC model(s), by February 2012 the global temperatures should have already increased to 14.75 degrees C (pink dotted line) based on a 12-month moving average. Instead, since 2000, the HadCRUT global temperature has only slightly increased (red dotted line).
Below is a synopsis of linear trends of the model prediction and actual observations:
- IPCC predicted: +4.0°C increase by year 2100
- Since 1/1/1990 actual: +1.3°C increase by year 2100
- Since 1/1/2000 actual: +0.4°C increase by year 2100
- Since 1/1/2002 actual: -0.7°C decrease by year 2100
Despite human CO2 emissions continuing to grow in a 'business-as-usual' manner (grey curve, black dots), global warming has stopped and is currently declining, as the blue columns of the chart indicate. The blue fitted trend curve reveals the current direction of global temperatures - 'global cooling' would be the more accurate description for the last 10 years.
Conclusion: Is global warming happening?
Global warming has monotonously creeped to a point of global cooling since the 1998 peak temperatures. CO2 levels appear to have little, if any, direct impact on direction or magnitude of changes in global temperatures.
Why has global warming turned to cooling or, as some prefer, "stalled"? For the confusion that reigns over that issue read here.
[Note: To calculate rolling 12-month average of HadCRUT absolute temperatures, 'C3' used the HadCRUT global monthly anomalies plus the monthly absolutes found here. 'By year 2100' increases/decrease calculated using the 12-mth moving average absolutes. Although the A1F1 scenario starts in year 2000, the above Excel chart includes data back to 1990 to provide a visual context. Additional info on emission scenarios.]