RealClimate

Climate science from climate scientists...

You are here: Home / Archives for Stefan

Stefan

What drives uncertainties in adapting to sea-level rise?

by

Guest article by Sally Brown, University of Southampton

Let me get this off my chest – I sometimes get frustrated at climate scientists as they love to talk about uncertainties! To be sure, their work thrives on it. I’m someone who researches the projected impacts and adaptation to sea-level rise and gets passed ‘uncertain’ climate data projections to add to other ‘uncertain’ data projections in my impact modellers work bag. But climate scientists do a good job. Without exploring uncertainties, science loses robustness, but uncertainties in combination can become unbounded and unhelpful to end users.

Let’s take an adaptation to sea-level rise as an example: With increasing scientific knowledge, acceptance and mechanisms that would allow adaptation to potentially occur, one would think that adaptation would be straight forward to implement. Not so. Instead of hard and fast numbers, policy makers are faced with wide ranges of uncertainties from different sources, making decision making challenging. So what uncertainties are there in the drivers of change, and can understanding these uncertainties enable better decisions for adaptation?

Prior to considering adaptation in global or regional models, or implementation at local level, drivers of change and their impacts (and thus uncertainties) require analysis – here are a few examples. [Read more…] about What drives uncertainties in adapting to sea-level rise?

Millennia of sea-level change

by

How has global sea level changed in the past millennia? And how will it change in this century and in the coming millennia? What part do humans play? Several new papers provide new insights.

2500 years of past sea level variations

This week, a paper will appear in the Proceedings of the National Academy of Sciences (PNAS) with the first global statistical analysis of numerous individual studies of the history of sea level over the last 2500 years (Kopp et al. 2016 – I am one of the authors). Such data on past sea level changes before the start of tide gauge measurements can be obtained from drill cores in coastal sediments. By now there are enough local data curves from different parts of the world to create a global sea level curve.

Let’s right away look at the main result. The new global sea level history looks like this:

Kopp2016_Fig1a+sat

Fig. 1 Reconstruction of the global sea-level evolution based on proxy data from different parts of the world. The red line at the end (not included in the paper) illustrates the further global increase since 2000 by 5-6 cm from satellite data. [Read more…] about Millennia of sea-level change

References

  1. R.E. Kopp, A.C. Kemp, K. Bittermann, B.P. Horton, J.P. Donnelly, W.R. Gehrels, C.C. Hay, J.X. Mitrovica, E.D. Morrow, and S. Rahmstorf, "Temperature-driven global sea-level variability in the Common Era", Proceedings of the National Academy of Sciences, vol. 113, 2016. http://dx.doi.org/10.1073/pnas.1517056113

Blizzard Jonas and the slowdown of the Gulf Stream System

by

Blizzard Jonas on the US east coast has just shattered snowfall records. Both weather forecasters and climate experts have linked the high snowfall amounts to the exceptionally warm sea surface temperatures off the east coast. In this post I will examine a related question: why are sea surface temperatures so high there, as shown in the snapshot from Climate Reanalyzer below?

 

GFS-025deg_NH-SAT1_SST_anom_24_Jan_2016

I will argue that this warmth (as well as the cold blob in the subpolar Atlantic) is partly due to a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), sometimes referred to as the Gulf Stream System, in response to global warming. There are two points to this argument:

[Read more…] about Blizzard Jonas and the slowdown of the Gulf Stream System

Bjørn Lomborg, just a scientist with a different opinion?

by

Bjørn Lomborg is a well-known media personality who argues that there are more important priorities than reducing emissions to limit global warming. In a recent controversy centering on him, the Australian government (known for its contradictory position on climate change) offered the University of Western Australia (UWA) $4 million to make Lomborg professor – which UWA first accepted, but then after massive protest from its staff and students refused. The Australian government was quick to label it a “freedom of speech” issue that Lomborg should get a university position, and vowed to find another university that would host him. However, free speech doesn’t guarantee everyone a university position; there are also academic qualifications required.

A translation of this post in Spanish is available here.
[Read more…] about Bjørn Lomborg, just a scientist with a different opinion?

Heaven belongs to us all – the new papal encyclical

by

Guest post by Brigitte Knopf

With his encyclical “Laudato Si” the Pope has written more than a moral appeal without obligation. He has presented a pioneering political analysis with great explosive power, which will probably determine the public debate on climate change, poverty and inequality for years to come. Thus, the encyclical is also highly relevant to me as a non-Catholic and non-believer; the implications of the encyclical are very apparent through the eyes of a secular person.

The core of the encyclical makes clear that global warming is a “global problem with grave implications: environmental, social, economic, political and for the distribution of goods” (25 – where the numbers refer to the numbering in the encyclical). The reasons identified are mainly the current models of production and consumption (26). The encyclical emphasizes that the gravest effects of climate change and the increasing inequality are suffered by the poorest (48). Since we face a complex socio-ecological crisis, strategies for a solution demand an integrated approach to combating poverty (139). So far, however, governments have not found a solution for the over-exploitation of the global commons, such as atmosphere, oceans, and forests (169). Therefore, the encyclical focusses on actors, such as non-governmental organizations, cooperatives and intermediate groups (179) and calls for a dialogue between politics, science, business and religion.

The encyclical is, with 246 individual points, too extensive to be discussed in here in its entirety, but three aspects are particularly noteworthy:

  1. it is based unequivocally onthe scientific consensusthat global warmingis taking placeand that climate changeis man-made; itrejects thedenialof anthropogenicwarming;
  2. it unmasks the political and economic structures of power behind the climate change debate and stresses the importance of non-state actors in achieving change; and
  3. it defines the atmosphere and the environment as a common good rather than a “no man’s land”, available for anyone to pollute. This underlines that climate change is strongly related to the issues of justice and property rights.

[Read more…] about Heaven belongs to us all – the new papal encyclical

Debate in the noise

by

Last week there was an international media debate on climate data which appeared to be rather surreal to me. It was claimed that the global temperature data had so far shown a “hiatus” of global warming from 1998-2012, which was now suddenly gone after a data correction. So what happened?

One of the data centers that compile the data on global surface temperatures – NOAA – reported in the journal Science on an update of their data. Some artifacts due to changed measurement methods (especially for sea surface temperatures) were corrected and additional data of previously not included weather stations were added. All data centers are continually working to improve their database and they therefore occasionally present version updates of their global series (NASA data are currently at version 3, the British Hadley Centre data at version 4). There is nothing unusual about this, and the corrections are in the range of a few hundredths of a degree – see Figure 1. This really is just about fine details. [Read more…] about Debate in the noise

A hypothesis about the cold winter in eastern North America + Update

by

The past winter was globally the warmest on record. At the same time it set a new cold record in the subpolar North Atlantic – and it was very cold in the eastern parts of North America. Are these things related?

Two weeks ago NOAA published the following map of temperature anomalies for the past December-January-February (i.e. the Northern Hemisphere winter). One week ago, we published a paper in Nature Climate Change (which had been in the works for a few years) arguing that the cold in the subpolar North Atlantic is indicative of an AMOC slowdown (as discussed in my last post). Immediately our readers started to ask (as we indeed had been asking ourselves): does the cold winter in eastern North America (culminating in the Inhofe snowball incident) have anything to do with what is going on in the Atlantic?

Winter15NOAAFig. 1 Temperature anomaly map for the past december-january-february, from NOAA.

[Read more…] about A hypothesis about the cold winter in eastern North America + Update

References

  1. S. Rahmstorf, J.E. Box, G. Feulner, M.E. Mann, A. Robinson, S. Rutherford, and E.J. Schaffernicht, "Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation", Nature Climate Change, vol. 5, pp. 475-480, 2015. http://dx.doi.org/10.1038/nclimate2554

What’s going on in the North Atlantic?

by

The North Atlantic between Newfoundland and Ireland is practically the only region of the world that has defied global warming and even cooled. Last winter there even was the coldest on record – while globally it was the hottest on record. Our recent study (Rahmstorf et al. 2015) attributes this to a weakening of the Gulf Stream System, which is apparently unique in the last thousand years.

The whole world is warming. The whole world? No! A region in the subpolar Atlantic has cooled over the past century – unique in the world for an area with reasonable data coverage (Fig. 1). So what’s so special about this region between Newfoundland and Ireland?

Rahmstorf_2015_1rc

Fig. 1 Linear temperature trend from 1900 to 2013. The cooling in the subpolar North Atlantic is remarkable and well documented by numerous measurements – unlike the cold spot in central Africa, which on closer inspection apparently is an artifact of incomplete and inhomogeneous weather station data.

[Read more…] about What’s going on in the North Atlantic?

Severe Tropical Cyclone Pam and Climate Change

by

Guest post by Kerry Emanuel

In the past 16 months, two exceptionally intense tropical cyclones, Haiyan and Pam, have struck the western Pacific with devastating effect. Haiyan may have had the highest wind speeds of any tropical cyclone on record, but we will never know for sure because we do a poor job estimating the intensity of storms that are not surveyed by aircraft. (Currently, only North Atlantic tropical cyclones are routinely reconnoitered by aircraft, and only if they threaten populated regions within a few days.) Pam’s analyzed intensity puts it within 10 knots of the most intense storms on record in the South Pacific, but here again this is within the error bars of satellite-derived intensity estimates.
pam2

[Read more…] about Severe Tropical Cyclone Pam and Climate Change

A new sea level curve

by

The “zoo” of global sea level curves calculated from tide gauge data has grown – tomorrow a new reconstruction of our US colleagues around Carling Hay from Harvard University will appear in Nature (Hay et al. 2015). That is a good opportunity for an overview over the available data curves. The differences are really in the details, the “big picture” of sea-level rise does not change. In all curves, the current rates of rise are the highest since records began.

The following graph shows the new sea level curve as compared to six known ones.

haysl1

Fig 1 Sea level curves calculated by different research groups with various methods. The curves show the sea level relative to the satellite era (since 1992). Graph: Klaus Bittermann.

All curves show the well-known modern sea level rise, but the exact extent and time evolution of the rise differ somewhat. Up to about 1970, the new reconstruction of Hay et al. runs at the top of the existing uncertainty range. For the period from 1880 AD, however, it shows the same total increase as the current favorites by Church & White. Starting from 1900 AD it is about 25 mm less. This difference is at the margins of significance: the uncertainty ranges overlap. [Read more…] about A new sea level curve

References

  1. C.C. Hay, E. Morrow, R.E. Kopp, and J.X. Mitrovica, "Probabilistic reanalysis of twentieth-century sea-level rise", Nature, vol. 517, pp. 481-484, 2015. http://dx.doi.org/10.1038/nature14093