Climate Sensitivity: A new assessment

Not small enough to ignore, nor big enough to despair. There is a new review paper on climate sensitivity published today (Sherwood et al., 2020 (preprint) that is the most thorough and coherent picture of what we can infer about the sensitivity of climate to increasing CO2. The paper is exhaustive (and exhausting – coming in at 166 preprint pages!) and concludes that equilibrium climate sensitivity is likely between 2.3 and 4.5 K, and very likely to be between 2.0 and 5.7 K. For those looking for some context

Denial and Alarmism in the Near-Term Extinction and Collapse Debate

Guest article by Alastair McIntosh,  honorary professor in the College of Social Sciences at the University of Glasgow in Scotland. This is an excerpt from his new book, Riders on the Storm: The Climate Crisis and the Survival of Being Mostly, we only know what we think we know about climate science because of the climate science. I have had many run-ins with denialists, contrarians or climate change dismissives as they are variously called. Over the past two years especially, concern has also moved to the other end of the spectrum, to alarmism. Both ends, while the latter has been more thinly tapered, can represent forms of denial. In this

Sensitive but unclassified: Part II

The discussion and analysis of the latest round of climate models continues – but not always sensibly. In a previous post, I discussed the preliminary results from the ongoing CMIP6 exercise – an international, multi-institutional, coordinated and massive suite of climate model simulations – and noted that they exhibited a wider range of equilibrium climate

Nenana Ice Classic 2020

Readers may recall my interest in phenological indicators of climate change, and ones on which $300K rest are a particular favorite. The Nenana Ice Classic is an annual tradition since 1917, and provides a interesting glimpse into climate change in Alaska. This year’s break-up of ice has just happened (unofficially, Apr 27, 12:56pm AKST), and, like in years past, it’s time to assess what the trends are. Last year was a record early break-up (on April 14th), and while this year was not as warm, it is still earlier than the linear trend (of ~8 days per

Update day 2020!

Following more than a decade of tradition (at least), I’ve now updated the model-observation comparison page to include observed data through to the end of 2019. As we discussed a couple of weeks ago, 2019 was the second warmest year in the surface datasets (with the exception of HadCRUT4), and 1st, 2nd or 3rd in satellite datasets (depending on which one). Since this year was slightly above the linear trends up to 2018, it

Surprised by the shallows – again

Guest commentary from Jim Acker (GSFC/Adnet) Research on the ocean carbonate cycle published in 2019 supports results from the 1980s – in contrast to many papers published since then. During my graduate school education and research program in the 1980s, conducted at the Department of Marine Science (now the College of Oceanography) of the University of South Florida in St. Petersburg, I participated in research on the production (biogenic calcification) and fate of calcium carbonate (CaCO3) in the open waters of the northern Pacific ocean. There were two primary aspects of this research: one, to measure the sinking flux of biogenic materials in the water column of the Pacific Ocean, and

More than 500 people misunderstand climate change

A consensus is usually established when one explanation is more convincing than alternative accounts, convincing the majority. This is also true in science. However, science-based knowledge is also our best description of our world because it is built on testing hypotheses that are independently reexamined by colleagues. It is also typical that there are a few stubborn people who think they know better than the rest. When it comes to climate science, there is a small group of people who refuse to acknowledge

Sensitive But Unclassified

The US federal government goes to quite a lot of effort to (mostly successfully) keep sensitive but unclassified (SBU) information (like personal data) out of the hands of people who would abuse it. But when it comes to the latest climate models, quite a few are SBU as well. The results from climate models that are being run for CMIP6 have been talked about for a few months as the papers describing them have made it in to the literature, and the first assessments of the multi-model ensemble have

10 years on

I woke up on Tuesday, 17 Nov 2009 completely unaware of what was about to unfold. I tried to log in to RealClimate, but for some reason my login did not work. Neither did the admin login. I logged in to the back-end via ssh, only to be inexplicably logged out again. I did it again. No dice. I then called the hosting company and told them to take us offline until I could see what was going on. When I did get control back from the hacker (and hacker it was), there was a large uploaded file on our server, and a draft post ready to

How good have climate models been at truly predicting the future?

A new paper from Hausfather and colleagues (incl. me) has just been published with the most comprehensive assessment of climate model projections since the 1970s. Bottom line? Once you correct for small errors in the projected forcings, they did remarkably well. Climate models are a core part of our understanding of our future climate. They also have been frequently attacked by those dismissive of climate change, who argue that since climate models are inevitably approximations they have no predictive power, or indeed, that they aren’t even scientific. In an upcoming paper in Geophysical Research Letters, Zeke Hausfather, Henri Drake, Tristan Abbott and I took a look at how well climate models have actually been

The Antarctic ice sheet is melting and, yeah, it’s probably our fault.

Glaciers in West Antarctica have thinned and accelerated in the last few decades. A new paper provides some of the first evidence that this is due to human activities. by Eric Steig It’s been some time since I wrote anything for RealClimate. In the interim there’s been a lot of important new work in the area of my primary research interest – Antarctica. Much of it is aimed at addressing the central question in Antarctic glaciology: How much ice is going to be lost from the West Antarctic ice sheet, and how soon?

Koonin’s case for yet another review of climate science

We watch long YouTube videos so you don’t have to. In the seemingly endless deliberations on whether there should be a ‘red team’ exercise to review various climate science reports, Scott Waldman reported last week that the original architect of the idea, Steve Koonin, had given a talk on touching on the topic at Purdue University in Indiana last month. Since the talk is online, I thought it might be worth a viewing. [Spoiler alert. It wasn’t]. The red team issue came up a few times. Notably Koonin says at one point in the Q and A: The reports are right. But obviously I would not be pushing a red team exercise

Can planting trees save our climate?

In recent weeks, a new study by researchers at ETH Zurich has hit the headlines worldwide (Bastin et al. 2019). It is about trees. The researchers asked themselves the question: how much carbon could we store if we planted trees everywhere in the world where the land is not already used for agriculture or cities? Since the leaves of trees extract carbon in the form of carbon dioxide – CO2 – from the air and then release the oxygen – O2 – again, this is a great climate protection measure

Nenana Ice Classic 2019

Wow. Perhaps unsurprisingly given the exceptional (relative) warmth in Alaska last month and in February, the record for the Nenana Ice Classic was shattered this year. The previous official record was associated with the exceptional conditions in El Niño-affected winter of 1939-1940, when the ice went out on April 20th 1940. Though since 1940 was a leap year, that was actually a little later (relative to the vernal equinox) than the ice out date in 1998 (which wasn’t a leap year).  Other records are also tumbling in the region, for instance the ice out data at Bethel, Alaska: The Kuskokwim River at Bethel has gone out. This is,

First successful model simulation of the past 3 million years of climate change

Guest post by Matteo Willeit, Potsdam Institute for Climate Impact Research A new study published in Science Advances shows that the main features of natural climate variability over the last 3 million years can be reproduced with an efficient model of the Earth system. The Quaternary is the most recent geological Period, covering the past ~2.6 million years. It is defined by the presence of glacial-interglacial cycles associated with the cyclic

Alpine glaciers: Another decade of loss

Guest Commentary by Mauri Pelto (Nichols College) Preliminary data reported from the reference glaciers of the World Glacier Monitoring Service (WGMS) in 2018 from Argentina, Austria, China, France, Italy, Kazakhstan, Kyrgyzstan, Nepal, Norway, Russia, Sweden, Switzerland and United States indicate that 2018 will be the 30th consecutive year of significant negative annual balance (> -200mm); with a mean balance of -1247 mm for the 25 reporting reference glaciers, with only one glacier reporting a positive mass balance (WGMS, 2018). A view

What the 2018 climate assessments say about the Gulf Stream System slowdown

Last year, twenty thousand peer reviewed studies on ‘climate change’ were published. No single person can keep track of all those – you’d have to read 55 papers every single day. (And, by the way, that huge mass of publications is why climate deniers will always find something to cherry-pick that suits their agenda.) That is why climate assessments are so important, where a lot of scientists pool their expertise and

Update day

So Wednesday was temperature series update day. The HadCRUT4, NOAA NCEI and GISTEMP time-series were all updated through to the end of 2018 (slightly delayed by the federal government shutdown). Berkeley Earth and the MSU satellite datasets were updated a couple of weeks ago. And that means that everyone gets to add a single additional annual

The best case for worst case scenarios

The “end of the world” or “good for you” are the two least likely among the spectrum of potential outcomes.Stephen Schneider Scientists have been looking at best, middling and worst case scenarios for anthropogenic climate change for decades. For instance, Stephen Schneider himself took a turn back in 2009. And others have postulated both far more rosy and far more catastrophic possibilities as well (with somewhat variable evidentiary bases). This question came up last year in the wake of a high

Mercury, the other geologically persistent planetary poison

The thing that really gets me in the gut about global warming from fossil fuel combustion is how long it will last. Carbon mined from the deep Earth and injected into the “fast carbon cycle” of the atmosphere, ocean, and land surface will continue to affect atmospheric CO2 concentrations, and climate, for hundreds of thousands of years into the future, unless we clean up the atmosphere ourselves. It turns out that human emissions of the element

Resplandy et al. correction and response

Guest commentary from Ralph Keeling (UCSD) I, with the other co-authors of Resplandy et al (2018), want to address two problems that came to our attention since publication of our paper in Nature last week. These problems do not invalidate the methodology or the new insights into ocean biogeochemistry on which it is based, but they do influence the mean rate of warming we infer, and more importantly, the uncertainties of that calculation. We would like to thank Nicholas Lewis for first bringing an apparent anomaly in the trend calculation to our attention. We quickly realized that our calculations incorrectly

The long story of constraining ocean heat content

Scientists predicted in the 1980s that a key fingerprint of anthropogenic climate change would be found in the ocean. If they were correct that increases in greenhouse gases were changing how much heat was coming into the system, then the component with the biggest heat capacity, the oceans, is where most of that heat would end up. We have now had almost two decades of attempts to characterize this change, but the path to confirming those predictions has been anything but smooth… Predictions At least as far back as Hansen et

Does a slow AMOC increase the rate of global warming?

Established understanding of the AMOC (sometimes popularly called Gulf Stream System) says that a weaker AMOC leads to a slightly cooler global mean surface temperature due to changes in ocean heat storage. But now, a new paper in Nature claims the opposite and even predicts a phase of rapid global warming. What’s the story? By Stefan Rahmstorf and Michael Mann In 1751, the captain of an English slave-trading