Visualising UK summer temperatures – what are the odds?

How will UK summer temperatures change in future? And, how might we best communicate the possibilities? This is a short post describing one effort in visualising the possible outcomes. Continue reading

Posted in observations, projections, temperature, uncertainty, variability, visualisation | 2 Comments

Top-of-atmosphere contribution to unforced variability in global temperature

As the attention received by the ‘global warming hiatus’ demonstrates, global mean surface temperature (T) variability on decadal timescales is of great interest to both the general public and to scientists. Here, I will discuss a recently published paper (Brown et al., 2014) that attempts to contribute to this scientific discussion by investigating the impact of unforced (internal) changes in the earth’s top-of-atmosphere (TOA) energy budget on decadal T variability.

Guest post by Patrick Brown (Duke University) Continue reading

Posted in GCMs, observations, temperature, uncertainty, variability | 5 Comments

Getting a Comment published in Nature

After our recent Brief Communication Arising (BCA) was published in Nature on Mora et al., several people have asked about the process involved in getting such a comment published.

Nature apparently only publish a small fraction of BCAs received and allow a reply from the original authors. Roughly one BCA is published online each month and they never appear in the print edition. This post describes what happened in our particular example. Continue reading

Posted in journals | 3 Comments

More Mora emergence issues

A previous post discussed the recent Comment on Mora et al., which considered mainly methodological & statistical errors. However, the erroneous assumptions regarding uncertainty in the Mora et al. study have further implications for their results on population and income.

Guest post from Flavio Lehner (Uni. Bern) Continue reading

Posted in emergence, GCMs, projections, uncertainty, variability | 2 Comments

On Mora et al.’s Reply

Yesterday saw the publication of our Comment on Mora et al., along with Mora et al.’s Reply and an associated ‘News & Views’ piece. Although the Editors deserve credit for commissioning a News & Views piece on this exchange – a first for a Comment in Nature – there are still errors in Mora et al.’s Reply. A previous post summarised the issues with the original paper, and Doug McNeall also discusses the main issues. Continue reading

Posted in climate sensitivity, emergence, journals, uncertainty, variability | 17 Comments

Uncertainties in the timing of unprecedented climates

Back in October 2013, Nature published an analysis by Camilo Mora et al. which discussed when ‘unprecedented climates’ would emerge, with a focus on regions of high biodiversity.

The paper was highlighted by Nature with an associated News & Views article and received widespread media attention (e.g. Climate Central, National Geographic, Guardian, Grist, amongst many). The paper was also in the top 100 most discussed papers from 2013 according to Altmetric.

Unfortunately, it has since emerged that the analysis has some serious flaws. A ‘Brief Communication Arising’ (or Comment) has now been published by Hawkins et al. in Nature (freely available for one month), written by a large group which includes several IPCC Lead Authors, from both WG1 and WG2. There is also a ‘Reply’ from Mora et al., and a new News & Views (N&V) piece by Scott Power discussing the continuing disagreement between the author teams. This is the first ever N&V on a Comment in Nature.

This post provides a slightly less technical description of the issues with Mora et al.’s analysis. The errors in Mora et al.’s Reply are summarised in a separate post. The Carbon Brief blog has also produced some videos on the topic. Continue reading

Posted in emergence, GCMs, IPCC AR5, projections, temperature, uncertainty, variability | 10 Comments

The signal, the noise & the time of emergence

Temperatures have increased over most parts of the planet, but this signal is somewhat obscured by the random noisy fluctuations of natural climate variability. The year in which we can we detect the ‘signal’ of temperature change in the presence of the ‘noise’ is often called the ‘time of emergence’. This is the first of a series of posts on this topic this week. Continue reading

Posted in emergence, observations, temperature, variability | 15 Comments

Improving the weather from 96 years ago

Ideally, we would have observations of past weather everywhere for several centuries to reconstruct the state of the atmosphere and learn about its variability. But, we don’t.

Instead, all the observations ever taken would, ideally, be available digitally for everyone to use. But, they aren’t. Many past observations are buried in hand-written journals and logbooks, gathering dust in libraries and archives all over the world. Rescuing this data would be of great benefit to reconstructing past weather, as this example will show. Continue reading

Posted in observations, uncertainty, weather | Leave a comment

Predictable September Arctic sea-ice minimum?

Arctic sea-ice extent varies considerably from year-to-year, especially in the summer. Skillful forecasts of the expected extent could be valuable to a wide range of Arctic stakeholders. But, how predictable is the Arctic sea-ice extent in summer? And, can more complex sea-ice models with improved representations of key physical processes improve forecasts? Continue reading

Posted in Arctic, predictability, sea-ice, variability | 4 Comments

When will we reach 2°C?

A change in global surface temperature to 2°C above pre-industrial climate is often used as a threshold for ‘dangerous climate change’. Although impacts will tend to get worse as temperatures increase, there is no clear evidence yet of such a sharp threshold in the climate. However, the 2°C threshold seems to be useful to policymakers. So, when might we expect to reach this threshold and have any regions experienced such a change already? Continue reading

Posted in emergence, observations, temperature, variability, visualisation | 4 Comments

Demonstrating climate variability

Communicating climate variability has become an important issue with the recent slowdown in global surface temperature rise. Below are some examples of different aspects of communicating these issues, with a focus on regional spatial scales, but more examples would be welcomed! What works, and what doesn’t? Continue reading

Posted in variability, visualisation | 11 Comments

Comments on the GWPF climate sensitivity report

Guest post by Piers Forster, with comments from Jonathan Gregory & Ed Hawkins

Lewis & Crok have circulated a report, published by the Global Warming Policy Foundation (GWPF), criticising the assessment of equilibrium climate sensitivity (ECS) and transient climate response (TCR) in both the AR4 and AR5 IPCC assessment reports.

Climate sensitivity remains an uncertain quantity. Nevertheless, employing the best estimates suggested by Lewis & Crok, further and significant warming is still expected out to 2100, to around 3°C above pre-industrial climate, if we continue along a business-as-usual emissions scenario (RCP 8.5), with continued warming thereafter. However, there is evidence that the methods used by Lewis & Crok result in an underestimate of projected warming. Continue reading

Posted in climate sensitivity, GCMs, IPCC AR5, observations, projections, temperature, uncertainty | 223 Comments

The cascade of uncertainty in climate projections

Climate projections have demonstrated the need to adapt to a changing climate, but have been less helpful (so far) in guiding how to effectively adapt. Part of the reason is the ‘cascade of uncertainty’ going from assumptions about future global emissions of greenhouse gases to what that means for the climate to real decisions on a local scale. Each of the steps in the process contains uncertainty, but which step is the most important? And, how might this be visualised? Continue reading

Posted in projections, temperature, uncertainty, variability, visualisation | 11 Comments

The future of the slowdown

Imagine it is 2031, and the IPCC is preparing to release its 8th Assessment Report. How does the recent slowdown in global mean surface temperature rise look? As this largely depends on how fast the climate warms from 2014 onwards, we can explore a range of possibilities. Continue reading

Posted in observations, projections, temperature, visualisation | 25 Comments

Atlantic overturning in decline?

Recent direct observations of the strength of the Atlantic Meridional Overturning Circulation (AMOC) show a decline of 10-15% since 2004. Is this a temporary fluctuation or part of a longer-term decline? A new analysis suggests that we might expect a further decline in the AMOC over the coming decade, which could impact on the climate of Europe and beyond. Continue reading

Posted in Atlantic, MOC, observations, variability | 4 Comments

The future of white Christmases

It’s December, which means the usual discussion as to whether or not it will be a white Christmas. You can even bet on it. But, how might these odds change in future? Are children going to know what snow is? Continue reading

Posted in projections, variability, weather | 2 Comments

Updates to comparison of CMIP5 models & observations

As 2013 is nearly over, it is time for a short update to the comparisons of CMIP5 models and observations for global mean surface air temperatures. Part of the motivation for an update is the Cowtan & Way paper on spatial coverage biases in HadCRUT4, which has been given prominent attention in blogs and the media, notably the front page of The Independent. Continue reading

Posted in IPCC AR5, projections, temperature | 5 Comments

Effects of recent observed vs RCP forcings

The recent global temperature hiatus has been explained by the IPCC AR5 as partly due to natural radiative forcings (solar & volcanic effects) and internal variability. Recently, other effects such as CFCs and biases in the observational coverage have also been suggested, as well as continuing uncertainty about the regional effects of aerosol forcings. When comparing simulations and observations, the CMIP5 simulations tend to use projected forcings rather than observed forcings after 2005. But what effect does this have? Continue reading

Posted in GCMs, projections, temperature | 4 Comments

Sources of uncertainty in CMIP5 projections

The recent IPCC AR5 includes a discussion on the sources of uncertainty in climate projections (Fig. 11.8, section 11.3.1.1), which updates previous analyses using CMIP3 (temperature, precipitation) to the latest CMIP5 simulations. The dominant source of uncertainty depends on lead time, variable and spatial scale. Continue reading

Posted in GCMs, IPCC AR5, projections, temperature, uncertainty, variability, visualisation | 13 Comments

Time of emergence of a warming signal

The ‘signal’ of a warming climate is emerging against a background ‘noise’ of natural internal variability. Both the magnitude of the signal and the noise vary spatially and seasonally. As society and ecosystems tend to be somewhat adapted to natural variability, some of the impacts of any change will be felt when the signal becomes large relative to the noise. So, it is important to note where and when this might occur. Continue reading

Posted in emergence, GCMs, IPCC AR5, projections, temperature, uncertainty | 11 Comments

Near-term global surface temperature projections in IPCC AR5

The final version of the IPCC AR5 WG1 assessment on the physical basis for climate change has now been published. The AR5 includes, for the first time, a specific chapter and assessment on ‘near-term’ climate change, which covers the period up to 2050, but with a specific focus on the 2016-2035 period.

Continue reading

Posted in IPCC AR5, projections, temperature, uncertainty, variability | 25 Comments

Arctic sea ice extent in 2014

Following last year’s simple straw poll, a similar question for this year:

Will the Arctic sea ice extent for September 2014 be more or less than September 2013?

Hoping for views and expectations from public and scientists alike.

Continue reading

Posted in Arctic, predictability, sea-ice | 16 Comments

Near-term regional climate: the range of possibilities

What are the possible regional temperature trends over the coming few decades? Globally, on average, there is expected to be a long-term warming, but this is not necessarily true for any particular location or period. What are the probabilities of a local warming or cooling? Continue reading

Posted in GCMs, projections, temperature, uncertainty, variability, visualisation | 10 Comments

Recent slowdown in global surface temperature rise

The Science Media Centre recently held a briefing for journalists on the recent slowdown in global surface temperature rise, and published an accompanying briefing note. The Met Office also released three reports on the topic.

The key points were: (1) recent changes need to be put in longer term context & other climate indicators such as sea level, Arctic sea ice, snow cover, glacier melt etc are also important; (2) the explanation for recent slowdown is partly additional ocean heat uptake & partly negative trends in natural radiative forcing (due to solar changes and small volcanic eruptions) which slightly counteract the positive forcing from GHGs; (3) the quantification of the relative magnitude of these causes is still work in progress; (4) climate models simulate similar pauses. Continue reading

Posted in observations, temperature, uncertainty, variability, visualisation | 11 Comments

Lengthy simulated pauses in global mean surface temperature

A very simple question for this short post: what length pause (trend < 0) in global mean surface temperature could be simulated in a warming climate?

Continue reading

Posted in GCMs, temperature, variability | 19 Comments