Major PAGES 2k Network Paper Confirms the Hockey Stick 22 April 2013
"They find that over the past 2,000 years, until 100 years ago, the planet underwent a long-term cooling trend. There was a 'Medieval Warm Period', but different regions warmed at different times, and overall global surface temperatures were warmer at the end of the 20th century than during the MWP peak. The 2,000-year cooling trend has been erased by the warming over the past century. And of course more warming is yet to come from continuing human greenhouse gas emissions.
"It's also worth noting that according to the instrumental temperature record, average surface temperatures for 1982–2012 have been about 0.2°C hotter than the 1970–2000 average. That additional warming would put current global surface temperatures well above any other time over the past 2,000 years. The PAGES 2k team concludes,
"the global warming that has occurred since the end of the nineteenth century reversed a persistent long-term global cooling trend. The increase in average temperature between the nineteenth and twentieth centuries exceeded the temperature difference between all other consecutive centuries in each region, except Antarctica and South America."
I found this short sentence particularly cogent.
They also found warming was twice as rapid in the Northern than the Southern hemisphere, due again to ocean dampening, since there is more ocean mass in the Southern than Northern hemisphere.
Ocean warms more slowly than land. The more gradual southern Hemisphere warming is misleading. Because we've been so focused on air temperature, our measure of planetary heating indicates twice as much heating in the North. In reality the same heat has been beating down on the south, but we haven't been counting its absorption into water. In a way this is like glycemic load. Two foods can contain the same amount of sugar, but one will raise your blood sugar faster than the other. However in the end both jack up your blood sugar just as much, just not at the same rate. We've been underestimating the total long term impact of heat by just counting the fast rise. Of course in the body sugar is used up and insulin rises faster to cope with a bolus of sugar. The planet has no similar mechanism for dissipating heat.