The evidence is pretty clear that the globe is cooling on most time scales, and right now we are at one of the coolest points in the history of the earth. Looking first at the last 65 million years, since T-Rex was running around:
Global Temperature estimates over the last 65 million years based on oxygen isotope thermometry of deep-ocean sediment cores from many parts of the world. Data from Zachos et al (2001). Graph by Robert A. Rohde. READ MORE…
reblogged from Climate Etc.
Undersea volcanoes may be impacting long-term climate change
by Alan Longhurst
I think this paper on on ocean tides, sea-floor volcanoes and Milankevitch cycles is a game changer.
Mid-ocean ridge eruptions as a climate valve
Abstract. Seafloor eruption rates and mantle melting fueling eruptions may be influenced by sea level and crustal loading cycles at scales from fortnightly to 100 kyr. Recent mid-ocean ridge eruptions occur primarily during neap tides and the first 6 months of the year, suggesting sensitivity to minor changes in tidal forcing and orbital eccentricity. An ~100 kyr periodicity in fast-spreading seafloor bathymetry and relatively low present-day eruption rates at a time of high sea level and decreasing orbital eccentricity suggest a longer-term sensitivity to sea level and orbital variations associated with Milankovitch cycles. Seafloor spreading is considered a small but steady contributor of CO2 to climate cycles on the 100 kyr time scale; however, this assumes a consistent short-term eruption rate. Pulsing of seafloor volcanic activity may feed back into climate cycles, possibly contributing to glacial/interglacial cycles, the abrupt end of ice ages, and dominance of the 100 kyr cycle.
M. Tolstoy, Mid-ocean ridge eruptions as a climate valve, doi:10.1002/2014GL063015, Geophys. Res. Lett. 2015 [abstract] [manuscript]
A post at WUWT includes the press release from Columbia University
The AGU also issued a press release [link]
Source: On the likelihood of recent record warmth
Judith Curry’s conclusions regarding the much publicized paper by Mann et al. in Nature:
As I see it, this paper is a giant exercise in circular reasoning:
- Assume that the global surface temperature estimates are accurate; ignore the differences with the satellite atmospheric temperatures
- Assume that the CMIP5 multi-model ensemble can be used to accurately portray probabilities
- Assume that the CMIP5 models adequately simulate internal variability
- Assume that external forcing data is sufficiently certain
- Assume that the climate models are correct in explaining essentially 100% of the recent warming from CO2
In order for Mann et al.’s analysis to work, you have to buy each of these 5 assumptions; each of these is questionable to varying degrees.