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Urban Heat Islands and U.S. Temperature Trends

Filed under: — group @ 13 February 2013

Guest Commentary by Zeke Hausfather and Matthew Menne (NOAA)

The impact of urban heat islands (UHI) on temperature trends has long been a contentious area, with some studies finding no effect of urbanization on large-scale temperature trend and others finding large effects in certain regions. The issue has reached particular prominence on the blogs, with some claiming that the majority of the warming in the U.S. (or even the world) over the past century can be attributed to urbanization. We therefore set out to undertake a thorough examination of UHI in the Conterminous United States (CONUS), examining multiple ‘urban’ proxies, different methods of analysis, and temperature series with differing degrees of homogenization and urban-specific corrections (e.g. the GISTEMP nightlight method; Hansen et al, 2010). The paper reporting our results has just been published in the Journal of Geophysical Research.
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  1. D.E. Parker, "Climate: Large-scale warming is not urban", Nature, vol. 432, pp. 290-290, 2004.
  2. X. Yang, Y. Hou, and B. Chen, "Observed surface warming induced by urbanization in east China", J. Geophys. Res., vol. 116, 2011.
  3. J. Hansen, R. Ruedy, M. Sato, and K. Lo, "GLOBAL SURFACE TEMPERATURE CHANGE", Rev. Geophys., vol. 48, 2010.

2012 Updates to model-observation comparisons

Time for the 2012 updates!

As has become a habit (2009, 2010, 2011), here is a brief overview and update of some of the most discussed model/observation comparisons, updated to include 2012. I include comparisons of surface temperatures, sea ice and ocean heat content to the CMIP3 and Hansen et al (1988) simulations.
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Sea-level rise: Where we stand at the start of 2013 — Part 2

Filed under: — stefan @ 11 January 2013

This is Part 2 of my thoughts on the state of sea-level research. Here is Part 1.

Sea-level cycles?

A topic that keeps coming up in the literature is the discussion on a (roughly) 60-year cycle in sea level data; a nice recent paper on this is Chambers et al. in GRL (2012). One thing I like about this paper is its careful discussion of the sampling issue of the tide gauges, which means that variability in the tide gauges is not necessarily variability in the true global mean sea level (see Part 1 of this post). I want to add some thoughts on the interpretation of this variability. Consider this graph from my Response to Comments in Science (2007):

Fig. 1: Fifteen-year averages of the global mean temperature (blue, °C, GISS data) and rate of sea level rise (red, cm/year, Church&white data), both detrended.
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  1. D.P. Chambers, M.A. Merrifield, and R.S. Nerem, "Is there a 60-year oscillation in global mean sea level?", Geophysical Research Letters, vol. 39, pp. n/a-n/a, 2012.
  2. S. Rahmstorf, "Response to Comments on "A Semi-Empirical Approach to Projecting Future Sea-Level Rise"", Science, vol. 317, pp. 1866d-1866d, 2007.

Sea-level rise: Where we stand at the start of 2013

Filed under: — stefan @ 9 January 2013

Progress has been made in recent years in understanding the observed past sea-level rise. As a result, process-based projections of future sea-level rise have become dramatically higher and are now closer to semi-empirical projections. However, process-based models still underestimate past sea-level rise, and they still project a smaller rise than semi-empirical models.

Sea-level projections were probably the most controversial aspect of the 4th IPCC report, published in 2007. As an author of the paleoclimate chapter, I was involved in some of the sea-level discussions during preparation of the report, but I was not part of the writing team for the projections. At the core of the controversy were the IPCC-projections which are based on process models (i.e. models that aim to simulate individual processes like thermal expansion or glacier melt). Many scientists felt that these models were not mature and understated the sea-level rise to be expected in future, and the IPCC report itself documented the fact that the models seriously underestimated past sea-level rise. (See our in-depth discussion published after the 4th IPCC report appeared.) That was confirmed again with the most recent data in Rahmstorf et al. 2012.
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  1. S. Rahmstorf, G. Foster, and A. Cazenave, "Comparing climate projections to observations up to 2011", Environ. Res. Lett., vol. 7, pp. 044035, 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.

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