In the article they demonstrate that both state-dependence and the presence of tipping points produce signatures in the distribution of instantaneous and generalized (two-point) equilibrium climate sensitivity (ECS). This measure is widely used to estimate expected future global warming but that is still poorly quantified. Peter and Anna find signatures of state-dependence and multistability originating from dependence of both albedo and emissivity on temperature in a global energy balance, and a more complex climate model.
During the last 100 years hurricanes have become more frequent and more destructive, new research from the University of Copenhagen by Aslak Grinsted, Peter Ditlevsen from TiPES and Jens Hesselbjerg shows. The study has surveyed the most destructive hurricanes on the south- and east coast of the USA, using new calculation methods that show, unequivocally, a connection between climate change and the most destructive hurricanes. The study is now published in PNAS.
Climate change used to be obscured by the statistical uncertainty
The traditional way of calculating hurricane damage, in order to be able to compare hurricanes and follow their development over time, was to survey the subsequent cost of the damage done by each hurricane. In other words, what would a hurricane from the 1950s cost, if it made landfall today? Using this method, a typical find is that the majority of the rising tendency in damage can be attributed to the fact that there are more of us and we are more wealthy, and there is quite simply more costly infrastructure to suffer damage. But evidence of a climatic change in destructive force by hurricanes has been obscured by statistical uncertainty.
Hurricanes are becoming bigger, stronger and more dangerous – an improved calculation method now shows a clear tendency
Aslak Grinsted has calculated the historical figures in a new way. Instead of comparing single hurricanes and the damage they would cause today, he and his colleagues have assessed how big an area could be viewed as an “area of total destruction”. Meaning how large an area would you have to completely destroy in order to account for the financial loss. Simultaneously, this makes comparison between rural areas and more densely populated areas like cities easier, as the unit of calculation is now the same: The size of the “area of total destruction”.
The climate signal in the new method has suddenly become apparent
In previous studies it proved difficult to isolate the “climate signal”. The climate signal should be understood as the effect climate change has had on hurricane size, strength and destructive force. It lay hidden behind variations due to the uneven concentration of wealth and it was statistically uncertain whether there was anytendency in the destruction. But with the new method this doubt has been eradicated. The weather has indeed become more dangerous on the south- and east coast of the USA. Furthermore, the result obtained by the research team has turned out to be more congruent with the climate models we use to predict and understand the development in extreme weather. It fits with the physics, quite simply, that global warming has the effect that there is an increase in the force released in the most extreme hurricanes.
Susana Barbosa from INESC TEC participates in the work within package 1 of the TiPES project on analysing paleoclimate time series for the identification of early warning signal of abrupt climate transitions.
Grains of dust illustrate how fast a landscape is covered with ice after an ice age sets in.
The shift from a
relatively warm interglacial to proper ice age is a typical tipping point in
the climate system. The climate changes into another mode because dark ground
converts sunlight into heat, but snow and ice covers reflect a large amount of
energy back into space.
The last time such a
shift took place was 113.000 years ago, when the Eem interglacial ended and
frost once again conquered the northern hemisphere. During the next thousands
of years a large part of North America, Asia, the whole of Scandinavia and a
part of Northern Germany was covered in kilometer thick white ice – exactly
like Greenland is today.
How fast did this change happen?
The time scale on how a
landscape is covered at the end of an interglacial was not known until now when
a new method, developed by Physics of Ice, Climate and Earth (PICE) at the
Niels Bohr Institute, University of Copenhagen, shows that the grains of dust
which are always present in permanent ice can detail the picture of the changing
The technique was recently published in Nature Communications, and exploits the fact that dust which reaches an ice cap typically has been whirled up from dry areas without snow or ice. After it lands it is embedded in the yearly layers of snow which through thousands of years under its own pressure become a cover of ice. But large grains and small specks of dust seldom travel the same distances. The small ones might come from the other side of the planet whilst larger grains of dust typically blow in from local areas.
Postdoc Marius Simonsen
and colleagues analyzed dust from new drillings in a local ice cap on the
peninsula Renland, not far from Ittoqqortoormiit (Scoresbysund) in
Eastern Greenland. By comparing large grains of dust in the ice with local dust
from the area, they have mapped how fast Eastern Greenland was covered with ice
and snow at the end of the last interglacial.
“With this new method we finally retrieve information on how the ice advances. It gives us a link to data on how fast we enter an ice age in a way we have never had before,” says Marius Simonsen.
The results document that it took 2400 years to completely cover the coastal areas of Eastern Greenland with ice and snow. In other words: It is a relatively slow process.
“It looks very much like we imagined it would. But these numbers are good to know. This is the first time we know with confidence how quickly Greenland becomes covered with snow. That can be built into climate models, so they can calculate in larger detail how these large shifts happen in the climate system,” explains Helle Astrid Kjær from TiPES.
Next step will be to
conduct similar analyses on ice from The Mueller Ice Cap in Eastern Canada and
maybe also The Hans Tausen Ice Cap on the tip of Eastern Greenland. Data, which
might give us an idea on whether the speed of the ice age might have varied
between geographical areas.
Contributors to ReCap are Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark; Department of Earth and Environmental Sciences, University Milano-Bicocca, Milan, Italy; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA; Department of Earth and Environmental Sciences, Columbia University, New York, NY, USA; Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark; Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania, USA; Danish Meteorological Institute, Copenhagen, Denmark.
Drilling of the ice core ReCap was supported by The Danish National Research Foundation, the American National Science Foundation, the German Alfred Wegener Institute and the European Union Horizon 2020 Research and Innovation Programme. The measurements of dust were supported by the EU funding ice2ice.
The TiPES project has received funding from the
European Union’s Horizon 2020 research and innovation programme under grant agreement No 820970.
Current climate models are unable to predict sudden and violent changes to climate, known as tipping points. This is a phenomenon that researchers fear more and more, and that the United Nations Intergovernmental Panel on Climate Change seeks answers to. As such, the University of Copenhagen is opening a new research center to, among other things, develop better climate models which more accurately predict the risk of climate system tipping points.
Global warming may reach a threshold in the very near future, one that triggers a sudden, violent shift in the climate system, one that catalyzes a domino effect of dramatic new climatic changes via feedback mechanisms. In other words, Earth’s climate could run amok in a self-perpetuating and spiraling trend that is impossible to slow or reverse. These phenomena are called “tipping points” because they describe the tipping of climate from one stable state to another. The most sophisticated of current climate models are unable to predict tipping points. No one knows whether these tipping points will be triggered by a temperature rise of 2 or 1.5?C degrees, or somewhere else along the scale.
“Researchers are increasingly concerned by tipping points – points of no return where climate will change dramatically regardless of our actions. A point where we could suck all of the CO2 out of the atmosphere and still be headed into the abyss. Our knowledge about this phenomenon is too limited. It is crucial for us to better inform the world’s decision makers. As things stand now, politicians are gearing up to respond to a gradual and steady rise of up to two degrees Celsius,” according to Peter Ditlevsen, a physicist and climate researcher at the Niels Bohr Institute and head of the new TiPES research center (Tipping Points in the Earth System).
When the Amazon dries
Peter Ditlevsen will head a large collaborative effort among eighteen European research institutions. Over the next four years, the research consortium will calculate tipping point thresholds, identify the climate system components most susceptible to tipping and develop new climate models. The consortium has a broad composition that includes climate model creators, mathematicians, geophysicists and even political decision-making experts. They have just signed a contract with the European Union for 65 million kroner in funding from the Horizon 2020 programme.
A familiar example of a potential tipping point is the point at which the melting of the Greenlandic ice sheet can no longer be halted. Such a point would catalyze a chain reaction of elevated seal levels, flooding and changed ocean circulation patterns. Another tipping point feared by scientists is that increasing drought will cause the Amazon rainforest to dry out, so that instead of absorbing huge amounts of CO2 and creating atmospheric oxygen, the forest would become a releaser of CO2.
“We don’t know how much the temperature needs to rise before a tipping point is reached. For example, we just don’t know what the limit is before Greenland’s ice sheet disappears permanently. It may have already been reached. Therefore, there is an urgency to learn more about the mechanisms of this type of violent climate change and develop improved climate models. This is precisely what we will be doing,” says Peter Ditlevsen.
Climate models not quite there
The large-scale climate models used today are only geared to calculate climate based on the past 100 years. They work from stable, linear climate developments. While these models have grown to incorporate more and more factors, and have improved significantly over the past 30 years, they still don’t reflect reality when it comes to large, non-linear changes or tipping points.
Several prehistoric examples of tipping points exist, including a 10-15?C average temperature increase over a 10-year span during the Ice Age. The periods preceding these tipping points resembled the even climate development we are now experiencing. As such, researchers will investigate past climate change using ice core samples and other methods.
TiPES is a collaborative research project between the University of Copenhagen; University of Exeter (UK); Potsdam Institute for Climate Impact Ressearch (DE); Complutense University of Madrid (ES); The University of Reading (UK); University of Bern (CH); Utrecht University (NL); United Kingdom Research and innovation, Natural Environment Research Council, British Antarctic Survey (UK); Université Catholique de Louvain (BE); Technical University of Munich (DE); Consiglio Nazionale delle Ricerche (IT); Ecole Normale Supérieure (FR); The Arctic University of Norway (NO); The Institute for Systems and Computer Engineering, Technology and Science – INESC TEC (PT); University of Bristol (UK); Met Office, Climate, Cryosphere and Oceans Group (UK) and Amigo (IT).
TiPES will run for four years, beginning in September 2019. The project is funded by the EU’s Horizon 2020.
The TiPES center, under the Niels Bohr Institute, will open in September 2019 and is headed by Associate Professor Peter Ditlevsen.
Tipping points can best be described as critical thresholds where the climate system as a whole, or its components, referred to as tipping elements, transition from one stable state to another. This occurs by way of a drastic and irreversible change that catalyzes a domino effect of feedback mechanisms, resulting in a cascade of numerous dramatic changes.
Examples of potential tipping elements (components): Disturbances to South American and Asian monsoons, changes in Atlantic ocean currents, melting of the Antarctic, reductions in Arctic sea ice, drought and extreme rainfall in Africa’s Sahel, drought in the coniferous belts of northern Europe, North America and Siberia.