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How much CO2 your country can still emit, in three simple steps

Filed under: — stefan @ 6 August 2019

Everyone is talking about emissions budgets – what are they and what do they mean for your country?

Our CO2 emissions are causing global heating. If we want to stop global warming at a given temperature level, we can emit only a limited amount of CO2. That’s our emissions budget. I explained it here at RealClimate a couple of years ago:

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 humanity has emitted. That is because any additional amount of CO2 in the atmosphere will remain there for a very long time (to the extent that our emissions this century will like prevent the next Ice Age due to begin 50 000 years from now). That is quite different from many atmospheric pollutants that we are used to, for example smog. When you put filters on dirty power stations, the smog will disappear. When you do this ten years later, you just have to stand the smog for a further ten years before it goes away. Not so with CO2 and global warming. If you keep emitting CO2 for another ten years, CO2 levels in the atmosphere will increase further for another ten years, and then stay higher for centuries to come. Limiting global warming to a given level (like 1.5 °C) will require more and more rapid (and thus costly) emissions reductions with every year of delay, and simply become unattainable at some point.

In her recent speech at the French National Assembly, Greta Thunberg rightly made the emissions budget her central issue.

So let’s look at how the emissions budget concept can be used to guide policy on future emissions trajectories for countries.

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Can planting trees save our climate?

Filed under: — stefan @ 16 July 2019

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. The researchers estimated 200 billion tons of carbon could be stored in this way – provided we plant over a trillion trees.

The media impact of the new study was mainly based on the statement in the ETH press release that planting trees could offset two thirds of the man-made CO2 increase in the atmosphere to date. To be able to largely compensate for the consequences of more than two centuries of industrial development with such a simple and hardly controversial measure – that sounds like a dream! And it was immediately welcomed by those who still dream of climate mitigation that doesn’t hurt anyone.

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

Filed under: — stefan @ 3 April 2019

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 growth and decay of continental ice sheets in the Northern Hemisphere. Climate variations during the Quaternary are best seen in oxygen isotopes measured in deep-sea sediment cores, which represent variations in global ice volume and ocean temperature. These data show clearly that there has been a general trend towards larger ice sheets and cooler temperatures over the last 3 million years, accompanied by an increase in the amplitude of glacial-interglacial variations and a transition from mostly symmetry cycles with a periodicity of 40,000 years to strongly asymmetric 100,000-year cycles at around 1 million years ago.  However, the ultimate causes of these transitions in glacial cycle dynamics remain debated.

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

Filed under: — stefan @ 28 January 2019

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 discuss and assess and summarize the state of the art.

So let us have a quick look what last year’s climate assessments say about the much-discussed topic of whether the Atlantic Meridional Overturning Circulation (AMOC, a.k.a. Gulf Stream System) has already slowed down, as predicted by climate models in response to global warming.

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Does a slow AMOC increase the rate of global warming?

Filed under: — stefan @ 18 July 2018

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 ship made a historic discovery. While sailing at latitude 25°N in the subtropical North Atlantic Ocean, Captain Henry Ellis lowered a “bucket sea-gauge” down through the warm surface waters into the deep. By means of a long rope and a system of valves, water from various depths could be brought up to the deck, where its temperature was read from a built-in thermometer. To his surprise Captain Ellis found that the deep water was icy cold.

These were the first ever recorded temperature measurements of the deep ocean. And they revealed what is now known to be a fundamental feature of all the world oceans: deep water is always cold. The warm waters of the tropics and subtropics are confined to a thin layer at the surface; the heat of the sun does not slowly warm up the depths as might be expected. Ellis wrote:

“This experiment, which seem’d at first but mere food for curiosity, became in the interim very useful to us. By its means we supplied our cold bath, and cooled our wines or water at pleasure; which is vastly agreeable to us in this burning climate.”

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

Filed under: — stefan @ 11 June 2018

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% to 30%. Only a proportion of these winter excess deaths are directly related to low ambient temperatures (rather than other seasonal factors). Yet, it is reasonable to suspect that fewer people will die from cold as winters are getting milder with climate change. On the other hand, excess mortality from heat may also be high, with, for example, up to 70,000 additional deaths attributed to the 2003 summer heat wave in Europe. So, will the expected reduction in cold-related mortality be large enough to compensate for the equally anticipated increase in heat-related mortality under climate change? More »

Does global warming make tropical cyclones stronger?

Filed under: — stefan @ 30 May 2018

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 in terms of overall activity (10 +/- 3 named storms), with tropical Atlantic warmth constituting a favorable factor, but predicted El Nino conditions an unfavorable factor.  Meanwhile, the first named storm, Alberto, has gone ahead without waiting for the official start of the season.

In the long term, whether we will see fewer or more tropical cyclones in the Atlantic or in other basins as a consequence of anthropogenic climate change is still much-debated. There is a mounting consensus, however, that we will see more intense hurricanes. So let us revisit the question of whether global warming is leading to more intense tropical storms. Let’s take a step back and look at this issue globally, not just for the Atlantic. More »

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 that). But there were also some questions and criticisms in the media, so I’d like to present a forum here for discussing these questions and hope that others (particularly those with a different view) will weigh in in the comments section below. More »

Stronger evidence for a weaker Atlantic overturning circulation

Filed under: — stefan @ 11 April 2018

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 other problems such as rising sea levels and increasing heat waves, droughts and extreme precipitation. But is such a slowdown already underway today? This question is easier asked than answered. The Atlantic Meridional Overturning Circulation (AMOC, also known as Gulf Stream System) is a huge, three-dimensional flow system throughout the Atlantic, which fluctuates on different time scales. It is therefore by no means enough to put a current meter in the water at one or two points. More »

The global CO2 rise: the facts, Exxon and the favorite denial tricks

Filed under: — stefan @ 25 January 2018

The basic facts about the global increase of CO2 in our atmosphere are clear and established beyond reasonable doubt. Nevertheless, I’ve recently seen some of the old myths peddled by “climate skeptics” pop up again. Are the forests responsible for the CO2 increase? Or volcanoes? Or perhaps the oceans?

Let’s start with a brief overview of the most important data and facts about the increase in the carbon dioxide concentration in the atmosphere:

  1. Since the beginning of industrialization, the CO2 concentration has risen from 280 ppm (the value of the previous millennia of the Holocene) to now 405 ppm.
  2. This increase by 45 percent (or 125 ppm) is completely caused by humans.
  3. The CO2 concentration is thus now already higher than it has been for several million years.
  4. The additional 125 ppm CO2 have a heating effect of 2 watts per square meter of earth surface, due to the well-known greenhouse effect – enough to raise the global temperature by around 1°C until the present.

Fig. 1 Perhaps the most important scientific measurement series of the 20th century: the CO2 concentration of the atmosphere, measured on Mauna Loa in Hawaii. Other stations of the global CO2 measurement network show almost exactly the same; the most important regional variation is the greatly subdued seasonal cycle at stations in the southern hemisphere. This seasonal variation is mainly due to the “inhaling and exhaling” of the forests over the year on the land masses of the northern hemisphere. Source (updated daily): Scripps Institution of Oceanography. More »