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

Musing about Losing Earth

The NY Times Magazine has a special issue this weekend on climate change. The main article is “Losing the Earth” by Nathaniel Rich, is premised on the idea that in the period 1979 to 1989 when we basically knew everything we needed to know that climate change was a risk, and the politics had not yet been polarized, we missed our opportunity to act. Stated this way, it would probably

Are the heatwaves caused by climate change? 

I get a lot of questions about the connection between heatwaves and climate change these days. Particularly about the heatwave that has affected northern Europe this summer. If you live in Japan, South Korea, California, Spain, or Canada, you may have asked the same question. The raindrop analogy However, the question is inaccurate and I will try to explain this through an analogy. Let’s say I go for a walk with a friend and my friend feels a few drops of water that fall on her. She asks me if it’s raining. But as long as there was only few drops of water, it could also be something else. I tell her that we can get

Model Independence Day

We hold these truths to be self-evident, that all models are created equal, that they are endowed by their Creators with certain unalienable Rights, that among these are a DOI, Runability and Inclusion in the CMIP ensemble mean. Well, not quite. But it is Independence Day in the US, and coincidentally there is a new discussion paper (Abramowitz et al) (direct link) posted on model independence just posted at Earth System Dynamics

Will climate change bring benefits from reduced cold-related mortality? Insights from the latest epidemiological research

Guest post by Veronika Huber Climate skeptics sometimes like to claim that although global warming will lead to more deaths from heat, it will overall save lives due to fewer deaths from cold. But is this true? Epidemiological studies suggest the opposite. Mortality statistics generally show a distinct seasonality. More people die in the colder winter months than in the warmer summer months. In European countries, for example, the difference between the average number of deaths in winter (December – March) and in the remaining months of the year is 10%

30 years after Hansen’s testimony

“The greenhouse effect is here.” – Jim Hansen, 23rd June 1988, Senate Testimony The first transient climate projections using GCMs are 30 years old this year, and they have stood up remarkably well. We’ve looked at the skill in the Hansen et al (1988) (pdf) simulations before (back in 2008), and we said at the time that the simulations were skillful and that differences from observations would be clearer with a decade or two’s more data. Well, another decade has passed! How should we go

Does global warming make tropical cyclones stronger?

By Stefan Rahmstorf, Kerry Emanuel, Mike Mann and Jim Kossin Friday marks the official start of the Atlantic hurricane season, which will be watched with interest after last year’s season broke a number of records and e.g. devastated Puerto Rico’s power grid, causing serious problems that persist today. One of us (Mike) is part of a team that has issued a seasonal forecast (see Kozar et al 2012) calling for a roughly average season

Stronger evidence for a weaker Atlantic overturning circulation

Through two new studies in Nature, the weakening of the Gulf Stream System is back in the scientific headlines. But even before that, interesting new papers have been published – high time for an update on this topic. Let’s start with tomorrow’s issue of Nature, which besides the two new studies (one of which I was involved in) also includes a News&Views commentary. Everything revolves around the question of whether the Gulf Stream System has already weakened. Climate models predict this will be one consequence of global warming – alongside

The Alsup Aftermath

The presentations from the Climate Science tutorial last month have all been posted (links below), and Myles Allen (the first presenter for the plaintiffs) gives his impression of the events. Guest Commentary by Myles Allen A few weeks ago, I had an unusual — and challenging — assignment: providing a one-hour “tutorial” on the basic science of human-induced climate change to a Federal District Court in San

Nenana Ice Classic 2018

Another year, another ice out date. As in previous years, here’s an update of the Nenana Ice Classic time series (raw date, and then with a small adjustment for the calendrical variations in ‘spring’). One time series doesn’t prove much, but this is of course part of a much larger archive of phenomenological climate-related data that I’ve talked about before. This year the ice on the Tanana River went out on May 1st, oddly enough the same date as last year, after another very warm (but quite snowy) Alaskan winter. My shadow bet on whether any climate contrarian site will mention this dataset remains in play (none have

Climate indicators

The climate system is complex, and a complete description of its state would require huge amounts of data. However, it is possible to keep track of its conditions through summary statistics. There are some nice resources which give an overview of a number for climate indicators. Some examples include NASA and The Climate Reality Project. The most common indicator is the atmospheric background CO2 concentration, the global mean temperature, the global mean sea level, and the area with snow or Arctic sea ice. Other indicators include rainfall statistics, drought indices, or other hydrological aspects. The EPA provides some examples. One challenge has been that the state of the hydrological cycle is not as easily summarised

What did NASA know? and when did they know it?

If you think you know why NASA did not report the discovery of the Antarctic polar ozone hole in 1984 before the publication of Farman et al in May 1985, you might well be wrong. One of the most fun things in research is what happens when you try and find a reference to a commonly-known fact and slowly discover that your “fact” is not actually that factual, and that the real story is more interesting than you imagined… Here

A brief review of rainfall statistics

There have been a number of studies which show that we can expect more extreme rainfall with a global warming (e.g. Donat et al., 2016). Hence, there is a need to increase our resilience to more rainfall in the future. We can say something about how the rainfall statistics will be affected by a global warming, even when the weather itself is unpredictable beyond a few days. Statistics is remarkably predictable for a large number of events where each of them is completely random (welcome to thermodynamics and quantum physics). The normal distribution has often been used to describe the statistical character of daily temperature, but it is completely unsuitable for 24-hr precipitation. Instead, the gamma distribution has

O Say can you See Ice…

Some concerns about continued monitoring of sea ice by remote sensing were raised this week in Nature News an article in the (UK) Observer: Donald Trump accused of obstructing satellite research into climate change. The last headline is not really correct, but the underlying issues are real. What is this about? Since the late seventies, there have been almost continuous observations of polar sea ice by passive microwave sensing on multiple polar-orbiting satellites. This is the preferred technique since microwaves from the surface can penetrate clouds (which are abundant in the polar regions) and can

El Niño and the record years 1998 and 2016

2017 is set to be one of warmest years on record. Gavin has been making regular forecasts of where 2017 will end up, and it is now set to be #2 or #3 in the list of hottest years: With update thru September, ~80% chance of 2017 being 2nd warmest yr in the GISTEMP analysis (~20% for 3rd warmest). pic.twitter.com/k3CEM9rGHY — Gavin Schmidt (@ClimateOfGavin) October 17, 2017 In either case it will be the warmest year on record that was not boosted by El Niño. I’ve been asked several times whether that is surprising. After all, the El Niño event, which pushed up the 2016 temperature, is well

O Say Can You CO2…

Guest Commentary by Scott Denning The Orbiting Carbon Observatory (OCO-2) was launched in 2014 to make fine-scale measurements of the total column concentration of CO2 in the atmosphere. As luck would have it, the initial couple of years of data from OCO-2 documented a period with the fastest rate of CO2 increase ever measured, more than 3 ppm per year (Jacobson et al, 2016;Wang

Is there really still a chance for staying below 1.5 °C global warming?

There has been a bit of excitement and confusion this week about a new paper in Nature Geoscience, claiming that we can still limit global warming to below 1.5 °C above preindustrial temperatures, whilst emitting another ~800 Gigatons of carbon dioxide. That’s much more than previously thought, so how come? And while that sounds like very welcome good news, is it true? Here’s the key points. Emissions budgets – a very useful concept First of all – what the heck is an “emissions budget” for CO2? Behind this concept is the fact that the amount of global warming that is reached before temperatures stabilise depends (to good approximation) on the cumulative emissions of CO2, i.e. the grand total that

Impressions from the European Meteorological Society’s annual meeting in Dublin 

The 2017 annual assembly of the European Meteorological Society (EMS) had a new set-up with a plenary keynote each morning. I though some of these keynotes were very interesting. There was a talk by Florence Rabier from the European Centre for Medium-range Weather Forecasts (ECMWF), who presented the story of ensemble forecasting. Keith Seitter, the executive director of the American Meteorological Society (AMS), talked about the engagement with the

Data rescue projects

It’s often been said that while we can only gather new data about the planet at the rate of one year per year, rescuing old data can add far more data more quickly. Data rescue is however extremely labor intensive. Nonetheless there are multiple data rescue projects and citizen science efforts ongoing, some of which we have highlighted here before. For those looking for an intro into the subject, this 2014 article is an great introduction. Weather diary from the the Observatoire de Paris, written by Giovanni Cassini on 18th January 1789. I was asked this week whether there was a list of these projects, and with a bit of

Sensible Questions on Climate Sensitivity

Guest Commentary by Cristian Proistosescu, Peter Huybers and Kyle Armour tl;dr  Two recent papers help bridge a seeming gap between estimates of climate sensitivity from models and from observations of the global energy budget. Recognizing that equilibrium climate sensitivity cannot be directly observed because Earth’s energy balance is a long way from equilibrium, the studies instead focus on what can be inferred about climate sensitivity from historical trends. Calculating a climate sensitivity from the simulations that is directly comparable with that observed shows both are consistent. Crucial questions remain, however, regarding how climate sensitivity will

Observations, Reanalyses and the Elusive Absolute Global Mean Temperature

One of the most common questions that arises from analyses of the global surface temperature data sets is why they are almost always plotted as anomalies and not as absolute temperatures. There are two very basic answers: First, looking at changes in data gets rid of biases at individual stations that don’t change in time (such as station

Joy plots for climate change

This is joy as in ‘Joy Division’, not as in actual fun. Many of you will be familiar with the iconic cover of Joy Division’s Unknown Pleasures album, but maybe fewer will know that it’s a plot of signals from a pulsar (check out this Scientific American article on the history). The length of the line is matched to the frequency of the pulsing so that successive pulses

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