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What is signal and what is noise?

Filed under: — rasmus @ 29 December 2012

The recent warming has been more pronounced in the Arctic Eurasia than in many other regions on our planet, but Franzke (2012) argues that only one out of 109 temperature records from this region exhibits a significant warming trend. I think that his conclusions were based on misguided analyses.

The analysis did not sufficiently distinguish between signal and noise, and mistaking noise for signal will give misguided conclusions.

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  1. C. Franzke, "On the statistical significance of surface air temperature trends in the Eurasian Arctic region", Geophysical Research Letters, vol. 39, pp. n/a-n/a, 2012.

A review of cosmic rays and climate: a cluttered story of little success

Filed under: — rasmus @ 25 December 2012

A number of blogs were excited after having leaked the second-order draft of IPCC document, which they interpreted as a “game-changing admission of enhanced solar forcing”.

However, little evidence remains for a link between galactic cosmic rays (GCR) and variations in Earth’s cloudiness. Laken et al. (2012) recently provided an extensive review of the study of the GCR and Earth’s climate, from the initial work by Ney (1959) to the latest findings from 2012.

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  1. B.A. Laken, E. Pallé, J. Čalogović, and E.M. Dunne, "A cosmic ray-climate link and cloud observations", J. Space Weather Space Clim., vol. 2, pp. A18, 2012.

Stronger regional differences due to large-scale atmospheric flow.

A new paper by Deser et al. (2012) (free access) is likely to have repercussions on discussions of local climate change adaptation. I think it caught some people by surprise, even if the results perhaps should not be so surprising. The range of possible local and regional climate outcomes may turn out to be larger than expected for regions such as North America and Europe.

Deser et al. imply that information about the future regional climate is more blurred than previously anticipated because of large-scale atmospheric flow responsible for variations in regional climates. They found that regional temperatures and precipitation for the next 50 years may be less predictable due to the chaotic nature of the large-scale atmospheric flow. This has implications for climate change downscaling and climate change adaptation, and suggests a need to anticipate a wider range of situations in climate risk analyses.

Although it has long been recognised that large-scale circulation regimes affect seasonal, inter-annual climate, and decadal variations, the expectations have been that anthropogenic climate changes will dominate on time scales longer than 50 years. For instance, an influential analysis by Hawking & Sutton (2009) (link to figures) has suggested that internal climate variability account for only about 20% of the variance over the British isles on a 50-year time scale.
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  1. C. Deser, R. Knutti, S. Solomon, and A.S. Phillips, "Communication of the role of natural variability in future North American climate", Nature Climate change, vol. 2, pp. 775-779, 2012.
  2. E. Hawkins, and R. Sutton, "The Potential to Narrow Uncertainty in Regional Climate Predictions", Bulletin of the American Meteorological Society, vol. 90, pp. 1095-1107, 2009.

El Nino’s effect on CO2 causes confusion about CO2′s role for climate change

Filed under: — rasmus @ 11 September 2012

Are the rising atmospheric CO2-levels a result of oceans warming up? And does that mean that CO2 has little role in the global warming? Moreover, are the rising levels of CO2 at all related to human activity?

These are claims made in a fresh publication by Humlum et al. (2012). However, when seeing them in the context of their analysis, they seem to be on par with the misguided notion that the rain from clouds cannot come from the oceans because the clouds are intermittent and highly variable whereas the oceans are just there all the time. I think that the analysis presented in Humlum et al. (2012) is weak on four important accounts: the analysis, the physics, reviewing past literature, and logic.

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  1. O. Humlum, K. Stordahl, and J. Solheim, "The phase relation between atmospheric carbon dioxide and global temperature", Global and Planetary Change, vol. 100, pp. 51-69, 2013.

Climate indices to watch

Filed under: — rasmus @ 31 August 2012

What is the most important climate condition to keep tabs on? We have recently mentioned the record-low Arctic sea-ice extent, but hurricanes this year seem to be getting the most attention because of timing ofHurricane Isaac (I know of no evidence suggesting that the Arctic sea-ice has such a direct impact on U.S. politics!).

In addition, the status of ENSO issued by NOAA on August 27, 2012, states that El Niño conditions are likely to develop during August or September 2012, although the present state is classified as ‘ENSO-neutral‘. El Niño has a strong influence on local economies and societies in fairly extensive regions of the world. ENSO is a natural phenomenon, but may change under a changing climate and is interesting to watch over the long term.

It’s important to avoid getting lost into single indicators, however, as the climate system is complex, with many different parts interacting with one another. The American Meteorological Society (AMS) recently put out a statement on climate change, referring to a wide range of different climate indicators (here is a link for the most common ones). The AMS is not alone – the National Academy for Sciences (NAS) is also concerned about our climate and its many aspects: A fairly recent movie called Climate change at the NAS Climate Change: Lines of Evidence provides a comprehensive overview.

Both AMS and NAS accounts provide a rich picture of many different aspects with many different (important) details, which make them fairly long and complicated. This is why simple indices sometimes are used – to convey a simple message. We need both, and that’s why the NAS video and the AMS statement are so valuable – at least for the readers who understand what they are talking about. I’m not sure that everybody does, though.

R-script for making pretty picture

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