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Observations, Reanalyses and the Elusive Absolute Global Mean Temperature

10 Aug 2017 by Gavin

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 location), and second, for surface temperatures at least, the correlation scale for anomalies is much larger (100’s km) than for absolute temperatures. The combination of these factors means it’s much easier to interpolate anomalies and estimate the global mean, than it would be if you were averaging absolute temperatures. This was explained many years ago (and again here).

Of course, the absolute temperature does matter in many situations (the freezing point of ice, emitted radiation, convection, health and ecosystem impacts, etc.) and so it’s worth calculating as well – even at the global scale. However, and this is important, because of the biases and the difficulty in interpolating, the estimates of the global mean absolute temperature are not as accurate as the year to year changes.

This means we need to very careful in combining these two analyses – and unfortunately, historically, we haven’t been and that is a continuing problem.

[Read more…] about Observations, Reanalyses and the Elusive Absolute Global Mean Temperature

Filed Under: Climate modelling, Climate Science, Instrumental Record, Scientific practice, statistics

Unforced Variations: August 2017

2 Aug 2017 by group

This month’s open thread.

Filed Under: Climate Science, Open thread

Joy plots for climate change

22 Jul 2017 by Gavin

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 are plotted almost on top of each other. For many years this kind of plot did not have a well-known designation until, in fact, April this year:

I hereby propose that we call these "joy plots" #rstats https://t.co/uuLGpQLAwY

— Jenny Bryan (@JennyBryan) April 25, 2017

So “joy plots” it is.

[Read more…] about Joy plots for climate change

Filed Under: Climate Science, Communicating Climate, Instrumental Record

The climate has always changed. What do you conclude?

20 Jul 2017 by Stefan

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? [Read more…] about The climate has always changed. What do you conclude?

Filed Under: Climate Science, Communicating Climate, Paleoclimate, skeptics

Red team/Blue team Day 1

15 Jul 2017 by group

From Russell Seitz:

Filed Under: Climate Science

Climate Sensitivity Estimates and Corrections

12 Jul 2017 by Gavin

You need to be careful in inferring climate sensitivity from observations.

Two climate sensitivity stories this week – both related to how careful you need to be before you can infer constraints from observational data. (You can brush up on the background and definitions here). Both cases – a “Brief Comment Arising” in Nature (that I led) and a new paper from Proistosescu and Huybers (2017) – examine basic assumptions underlying previously published estimates of climate sensitivity and find them wanting.

[Read more…] about Climate Sensitivity Estimates and Corrections

References

  1. C. Proistosescu, and P.J. Huybers, "Slow climate mode reconciles historical and model-based estimates of climate sensitivity", Science Advances, vol. 3, 2017. http://dx.doi.org/10.1126/sciadv.1602821

Filed Under: Carbon cycle, Climate modelling, Climate Science, Greenhouse gases, Instrumental Record, Paleoclimate

Unforced variations: July 2017

1 Jul 2017 by group

So, big news this week: The latest update to the RSS lower troposphere temperatures (Zeke at Carbon Brief, J. Climate paper) and, of course, more chatter about the red team/blue team concept. Comments?

Filed Under: Climate Science, Open thread

What do you need to know about climate?

14 Jun 2017 by rasmus

What do you need to know about climate in order to be in the best position to adapt to future change? This question was discussed in a European workshop on Copernicus climate services during a heatwave in Barcelona, Spain (June 12-14).

[Read more…] about What do you need to know about climate?

Filed Under: Climate impacts, Climate modelling, Climate Science, Communicating Climate, downscaling, Scientific practice, Solutions

Why global emissions must peak by 2020

2 Jun 2017 by Stefan

(by Stefan Rahmstorf and Anders Levermann)

In the landmark Paris Climate Agreement, the world’s nations have committed to “holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels”. This goal is deemed necessary to avoid incalculable risks to humanity, and it is feasible – but realistically only if global emissions peak by the year 2020 at the latest.

Let us first address the importance of remaining well below 2°C of global warming, and as close to 1.5°C as possible. The World Meteorological Organization climate report[i] for the past year has highlighted that global temperature and sea levels keep rising, reaching record highs once again in 2016. Global sea ice cover reached a record low, and mountain glaciers and the huge ice sheets in Greenland and Antarctica are on a trajectory of accelerating mass loss. More and more people are suffering from increasing and often unprecedented extreme weather events[ii], both in terms of casualties and financial losses. This is the situation after about 1°C global warming since the late 19th Century. [Read more…] about Why global emissions must peak by 2020

Filed Under: Climate Science, Greenhouse gases, Solutions

Unforced Variations: June 2017

1 Jun 2017 by group

Absolutely nothing of consequence happening today in climate news. Can’t think of what people could discuss…

Filed Under: Climate Science, Open thread

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