In Weather this month, a paper by Colin Clark discusses temperature data from two rural stations in Somerset (UK). These two stations show a cooling trend over the last two decades which Clark suggests is opposite to that expected. The associated editorial suggests that this is a controversial finding.
Much attention is rightly given to changes in global mean surface temperature – it is the key metric for assessing how our climate is changing and evaluating mitigation strategies. However, no-one directly experiences changes in global mean temperature – it is only through local variations that changes in climate are felt.
So, what have global temperatures ever done for us? Continue reading What have global temperatures ever done for us?
Uncertainty in climate projections arises from several different sources. For example, the future emissions scenario is not known, so the usual approach is to run several to compare plausible futures. In addition, each climate model produces a different change in climate. However, on regional spatial scales and for the next couple of decades, it is the internal variability of climate which dominates. These natural climate fluctuations provide an irreducible limit on the precision with which we can make predictions on such spatial and temporal scales – but how large is this limit? Continue reading Irreducible uncertainty in near-term climate projections
Was last year really the warmest on record? As soon as NOAA published its official announcement in January, this question invaded the web feeding blogs, online newspapers and forums with passionate discussions. Relevant or pointless? The question is not so much knowing whether or not a new record was broken. Should 2014 rank second or third, this wouldn’t change the big picture: last year, temperatures on our planet continued the existing long-term positive trend. On top of that, the story is a bit thicker than the one single number obtained when averaging near-surface air temperatures in time and space. So, 2014: year of extremes or warm year in a changing climate?
Trends in global mean temperature are not static through time. Changes due to radiative forcings are influenced by internal climate variability. A recent paper by Karl et al. concluded that:
the central estimate for the rate of warming during the first 15 years of the 21st century is at least as great as the last half of the 20th century. These results do not support the notion of a “slowdown” in the increase of global surface temperature.
Are these conclusions, based on comparing a few periods, correct? Continue reading A spectrum of global temperature trends
A new paper out this week in PLOS Biology uses some CMIP5 simulations of daily mean surface air temperature as part of a larger analysis on the change to future plant growing days. The description of the analysis suggests they have not used the simulations appropriately to arrive at their conclusions. Here I highlight a couple of possible pitfalls in using such data in impact studies. Continue reading How not to use daily CMIP5 data for impact studies
In a recent post on Climate Audit, Nic Lewis criticised Marotzke & Forster (2015, Nature) for applying circular logic to their arguments about forcing, feedbacks & global temperature trends. This is a guest post by Jochem Marotzke & Piers Forster replying to those criticisms. Continue reading Marotzke & Forster response
Imagine a ball bouncing down a bumpy hill. Gravity will ensure that the ball will head downwards. But, if the ball hits a bump at a certain angle it might move horizontally or even upwards for a time, before resuming its inevitable downward trajectory. This bouncing ball is an analogy for the behaviour of Arctic sea-ice.
Post based on Swart et al., Nature Climate Change, or see a less technical summary. Continue reading Arctic sea-ice decline erratic as expected
As we reach the end of a likely record breaking year for global temperatures, what might we expect for 2015? Continue reading Climate forecasts for 2015
In my recent post whether there is a ‘hiatus’ in global warming I left out the satellite observations of the lower troposphere. The reason for that was that the analysis of these is different from that of the near-surface series, and I considered the latter were more relevant. First, most of us live at ground level most of the time, and secondly this has traditionally been the main measure by which to gauge global warming. My conclusions were that there has been a positive trend since 1998, but no trend over the last 10 years. However, the natural variability of 10-year trends is so large that this is compatible with the positive long-term trend. The indicator of global warming with the best signal-to-noise ratio, ocean heat content, shows no sign of stopping over the last 10 years.
2014 was a warm year for much of Europe and the globe, and may end up being the warmest year on record globally. But, no-one experiences a global mean temperature directly, so how about more locally? Can the signal of a warming climate be seen?
“In the last few years the warming trend of the earth has stopped” is a common type of remark these days. Is that indeed the case, and can we conclude that the projections for the rest of the century are being overestimated? And if so, how come that large parts of Europe are expected to have the warmest year recorded in 2014? There is a chance that the global mean temperature will also be the highest in the series.
Guest post by Geert Jan van Oldenborgh, KNMI Continue reading Hiatuses in the rise of temperature
Model projections of heavy precipitation and temperature extremes include large uncertainties. However, disagreement between individual simulations primarily arises from internal variability, whereas models agree remarkably well on the forced signal.
Post based on Fischer et al., 2014, Geophys. Res. Lett.
Continue reading Projected changes of precipitation and temperature extremes
Investigations into the recent observed slower rate of global warming have largely been focussed on variability in the Pacific basin. Climate models also show similar slowdowns focussed in the Pacific (e.g. Meehl et al. 2011).
But, is this the only type of simulated slowdown? How different can regional patterns of temperature change be for the same global change? Continue reading The slowdown zoo