UPDATE: C also Fergus
An everygreen in denial land has been that natural variability covers all climate change. All of those econometrician types, and some of Eli's favorite crazy aunts are fond of this, but they are lumpers. There is no single natural variability.
The tropics, of course, are the region with the most species, the most biodiversity, a hell of a lot of people, and an almost unchanging climate. Why do the bunnies think that the tropics have the most species, the most biodiversity and so many people? It is a lot easier dealing with a constant climate than one that varies all over the place. For one thing you don't have to change your fur with the seasons. The flip side is that nature in the tropics is not so well structured to deal with even small changes. While variability is low, human climate forcing driving the system beyond its usual local limit is dangerous.
Of course, high latitudes are vulnerable exactly because climate variability there is so high. In that case one worries about damage that is hard to reverse from large excursions (things don't always break the way you want). If there is a really warm summer, and the permafrost goes really non perm, it's hard to dig the Alaska oil industry out of the muck.
A paper to be published tomorrow in Nature The projected timing of climate departure from recent variability by Camilo Mora and friends at the University of Hawaii that makes an important contribution by recognizing this issue. Well, it does come from Hawaii, one of the places with the most constant climate on earth. They examined historic climate using 140 years of data for the past, and Earth System Models for the future (You want data from the future? Sorry, that is not currently available). They define exceeding natural variability at any position as exceeding the limits of the 140 year data record for various periods of time. For reference RCP45 is an emissions scenario that brings the CO2 mixing ratio in 2100 to 538 ppmV
Here we present a new index of the year when the projected mean climate of a given location moves to a state continuously outside the bounds of historical variability under alternative greenhouse gas emissions scenarios. Using 1860 to 2005 as the historical period, this index has a global mean of 2069 (+18 years s.d.) for near-surface air temperature under an emissions stabilization scenario and2047 (+14 years s.d.)under a ‘business-as-usual’ scenario. Unprecedented climates will occur earliest in the tropics and among low-income countries, highlighting the vulnerability of global biodiversity and the limited governmental capacity to respond to the impacts of climate change. Our findings shed light on the urgency of mitigating greenhouse gas emissions if climates potentially harmful to biodiversity and society are to be prevented.The years when variability will be exceeded forever on an annual basis are shown in a) below, and on a monthly basis in b) below. Eli directs your attention to the summers in the Indian subcontinent and Southeast Asia.
the projected timing of the ocean’s climate departure was pushed forward to this decade when pH was considered alongside sea surface temperature. Global mean ocean pH moved outside its historical variability by 2008 (+3 years s.d.), regardless of the emissions scenario analysed.Eli wonders if Richard Tol would agree that this paper explicitly endorses the IPCC consensus?