Evidence based Global Warming

Following fast on the heels of the hottest Jan-May — and spring — in the temperature record, it’s also the hottest Jan-June on record in the NASA dataset [click on figure to enlarge].

It’s all the more powerful evidence of human-caused warming “because it occurs when the recent minimum of solar irradiance is having its maximum cooling effect,” as a recent must-read NASA paper notes.

Software engineer (and former machinist mate in the US Navy) Timothy Chase put together a spreadsheet using the data from NASA’s Goddard Institute for Space Studies (click here). In NASA’s dataset, the 12-month running average temperature record was actually just barely set in March — and then easily set in April and topped out in May.

It still seems likely that 2010 will be the hottest year on record, but NOAA now predicts that “La Niña conditions are likely to develop during July – August 2010.” If the La Niña comes fast and deep (as in 1998 and 2007), that could make it a close call in the NASA dataset — and even more so in the satellite record, which is much more sensitive to ENSO ( El Niño Southern oscillation).

Blue curve: 12-month running-mean global temperature. Note correlation with Nino index (red = El Nino, blue = La Nina). Large volcanoes (green) have a cooling effect for ~2 years. Source: “Global Surface Temperature Change,” by James Hansen et al., June 2010.

Interestingly, June was tied for the third hottest on record for NASA, but was essentially tied for the hottest June in the RSS satellite record (and second hottest in the constantly tweaked UAH satellite dataset).

Although I’m sure it’s just another coincidence, but Rutgers University’s Global Snow Lab again reports a record low snow cover in the entire northern hemisphere for the month of June (what appears to be a long term trend):