Pre-industrial anthropogenic CO2 emissions: How large?

Guest article by William Ruddiman Fifteen years after publication of Ruddiman (2003), the early anthropogenic hypothesis is still debated, with relevant evidence from many disciplines continuing to emerge. Recent findings summarized here lend support to the claim that greenhouse-gas emissions from early agriculture (before 1850) were large enough to alter atmospheric composition and global climate substantially. Marine isotopic stage (MIS) 19 is the closest orbital analog to the current MIS 1 interglaciation (Tzedakis et al., 2012), with similarly small changes in precession (εsinω) and nearly

If you doubt that the AMOC has weakened, read this

A few weeks ago, we’ve argued in a paper in Nature that the Atlantic overturning circulation (sometimes popularly dubbed the Gulf Stream System) has weakened significantly since the late 19th Century, with most of the decline happening since the mid-20th Century. We have since received much praise for our study from colleagues around the world (thanks for

The climate has always changed. What do you conclude?

Probably everyone has heard this argument, presented as objection against the findings of climate scientists on global warming: “The climate has always changed!” And it is true: climate has changed even before humans began to burn fossil fuels. So what can we conclude from that? A quick quiz Do you conclude… (1) that humans cannot change the climate? (2) that we do not know whether humans are to blame for global warming? (3) that global warming will not have any severe consequences? (4) that we cannot stop global warming? The answer Not

Climate Sensitivity Estimates and Corrections

You need to be careful in inferring climate sensitivity from observations. Two climate sensitivity stories this week – both related to how careful you need to be before you can infer constraints from observational data. (You can brush up on the background and definitions here). Both cases – a “Brief Comment Arising” in Nature (that I led) and a new paper from Proistosescu and Huybers (2017) –

Q & A about the Gulf Stream System slowdown and the Atlantic ‘cold blob’

Last weekend, in Reykjavik the Arctic Circle Assembly was held, the large annual conference on all aspects of the Arctic. A topic of this year was: What’s going on in the North Atlantic? This referred to the conspicuous ‘cold blob’ in the subpolar Atlantic, on which there were lectures and a panel discussion (Reykjavik University had invited me to give one of the talks). Here I want to provide a brief overview of the issues discussed. What is the ‘cold blob’?

The Snyder Sensitivity Situation

Nature published a great new reconstruction of global temperatures over the past 2 million years today. Snyder (2016) uses 61 temperature reconstructions from 59 globally diverse sediment cores and a correlation structure from model simulations of the last glacial maximum to estimate (with uncertainties) the history of global temperature back through the last few dozen ice ages cycles. There are multiple real things to discuss about this – the methodology, the relatively small number of cores being used (compared to what could have been analyzed), the age modeling etc. – and

Why correlations of CO2 and Temperature over ice age cycles don’t define climate sensitivity

We’ve all seen how well temperature proxies and CO2 concentrations are correlated in the Antarctic ice cores – this has been known since the early 1990’s and has featured in many high-profile discussions of climate change. EPICA Dome C ice core greenhouse gas and isotope records. The temperature proxies are water isotope ratios that can be used to estimate Antarctic temperatures and, via a scaling, the global values. The CO2 and CH4 concentration changes can be converted to radiative forcing in W/m2 based on standard formulas. These two timeseries can be correlated and the regression (in ºC/(W/m2))

Ice-core dating corroborates tree ring chronologies

Guest commentary from Jonny McAneney You heard it here first… Back in February, we wrote a post suggesting that Greenland ice cores may have been incorrectly dated in prior to AD 1000. This was based on research by Baillie and McAneney (2015) which compared the spacing between frost ring events (physical scarring of living growth rings by prolonged sub-zero temperatures) in the bristlecone pine tree ring chronology, and spacing between prominent acids in a suite of ice cores from both Greenland