Twenty years ago, the trend in annual mean global mean temperature became detectable. Ten years ago, regional seasonal mean temperature trends were becoming clear. Nowadays, we can see trends even in weather extremes. In this post I show trends in long-term meteorological station data for hot, cold and wet extremes, and share some thoughts on tropical cyclones and droughts. It is underpinned by a decade of studying these around the globe, often in collaboration with the WWA team. I make no claims for completeness: the world is large and complicated, and I simply do not know all the literature.
Guest post by Geert Jan van Oldenborgh
Continue reading Trends in extremes
The consequences of the Paris Agreement’s choice of the pre-industrial as its baseline have been discussed previously on this blog. This choice makes sense from a climate forcing perspective (as radiative forcings are measured with respect to a quasi-equilibrated state, and the well-observed recent past is not close to have finished responding to anthropogenic drivers). Looking back into the pre-industrial period, there are fewer instrumental observations of the temperature across the globe. So naturally our knowledge of the pre-industrial baseline temperature is uncertain.
Recent work, such as Hawkins et al. (2017) and Schurer et al. (2017), have looked to assess and quantify this uncertainty in light of future targets. The magnitude of this uncertainty, although small, becomes important when you consider the amount of warming left between today and the 1.5°C target. Continue reading Uncertainty in warming since pre-industrial times
Recent media headlines have again discussed the issue of whether climate models are overly sensitive to greenhouse gases. These headlines have misinterpreted a study by Millar et al. which was discussing carbon budgets to limit global temperature rise to 1.5°C above pre-industrial levels.
A recent study by Medhaug et al. analysed the issue of how the models have performed against recent observations at length and largely reconciled the issue. An overly simplistic comparison of simulated global temperatures and observations might suggest that the models were warming too much, but this would be wrong for a number of reasons. Continue reading Are the models “running too hot”?
For twenty years between 1883 and 1904, three intrepid weathermen lived at the top of Ben Nevis – the highest mountain in the UK – experiencing some of the worst weather the country has to offer.
Every hour, day and night, winter and summer, and whatever the weather, one of them would step outside and check the meteorological instruments, diligently recording the observations.
This was a uniquely Victorian-era endeavour. Science for the sake of science. Rather than exploring the world’s polar regions like some of their contemporaries, these Weathermen were exploring the atmosphere.
There was simply no other way of learning in detail about how the atmosphere changed with height without living at the top of a mountain. So that is what they did.
Continue reading Weathermen of Ben Nevis
One possible criticism of global temperature datasets is that before around 1900 the observed data is too sparse to reliably infer changes in global temperature. Although we cannot travel back in time to take extra measurements to fill the gaps we can test whether the available observations are enough. Continue reading Sparse coverage of temperature observations
[Updated: 21st February 2018]
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The visualisation technique of ‘small multiples’ is often used to communicate a simple message. The above example shows maps of temperature change from 1850-2017 – the overall warming trend is obvious even though the details are fuzzy. Continue reading Mapping global temperature change
The temporary slowdown in global temperatures in the early-2000s is still prompting significant scientific discussion. A recent Commentary on the topic by Fyfe et al. was summarised in an earlier post. In response, a recent post by Rahmstorf et al. reiterates some of the statistical arguments that we discussed briefly in our Commentary1, but misses the main point. Continue reading Slowdown discussion
We are all familiar with the usual metrics used to highlight that the climate is changing: surface air temperatures, sea level, sea surface temperatures and ocean heat content all rising, glaciers retreating, Arctic sea ice declining etc. But, there are also many other less well known sources of information about how our climate is changing, and many involve ‘citizen scientists’, who often didn’t realise the potential long-term benefits of the data they were collecting. Continue reading Observing long-term climatic changes with unusual sources