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 observations, temperature, variability, visualisation | 3 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 | 8 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 GCMs, IPCC AR5, projections, temperature, uncertainty | 8 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?

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Posted in GCMs, temperature, variability | 19 Comments

Rates of change in global temperatures

The recent WMO press release on the climate of the 2001-2010 period highlighted that global temperature change was accelerating. Although this could be a misleading statement, should we even be expecting global temperature changes to be accelerating at present? Continue reading

Posted in GCMs, observations, projections, temperature, uncertainty, variability | 6 Comments

Global temperature changes in WMO report

A recent press release by the World Meteorological Organisation (WMO) described recent global temperature changes, and highlighted extreme weather in the 2001-2010 period. Much of the press release is good, but here I will examine the accuracy of two statements. Continue reading

Posted in temperature | 19 Comments

Comparing global temperature observations and simulations, again

A recent comparison of global temperature observations and model simulations on this blog prompted a rush of media and wider interest, notably in the Daily Mail, The Economist & in evidence to the US House of Representatives. Given the widespread misinterpretation of this comparison, often without the correct attribution or links to the original source, a more complete description & update is needed. Continue reading

Posted in observations, projections, temperature, uncertainty, variability | 40 Comments

Variable variability

The latest global climate models (GCMs) have performed pre-industrial control simulations as part of the CMIP5 coordinated experiments. In these simulations there are no changes to radiative forcings, which are kept fixed at year 1850 values – all the variability is therefore generated internally to the climate system. How different can this variability be? Continue reading

Posted in temperature, variability | 3 Comments

Global temperatures: 75 years after Callendar

Could varying concentrations of atmospheric carbon dioxide cause the planet to warm and cool? This was a key question facing scientists from the mid-1800s onwards – not because of a concern over man-made emissions of CO2, but because of a desire to understand the causes of the ice ages (identified by Louis Agassiz in 1837).

Then, exactly 75 years ago, in April 1938, a little appreciated scientist, Guy Stewart Callendar, presented the first evidence that the planet had recently warmed. Callendar also suggested that changes in atmospheric CO2 had caused a large part of this observed warming. A new paper reanalyses Callendar’s work to mark the 75th anniversary of his landmark study. Continue reading

Posted in history, observations, temperature, variability | 24 Comments

Reliability of regional climate trends

Climate information for the future is usually presented in the form of scenarios: plausible and consistent descriptions of future climate without probability information. This suffices for many purposes, but for the near term, say up to 2050, scenarios of emissions of greenhouse gases do not diverge much and we could work towards climate forecasts: calibrated probability distributions of the climate in the future. Continue reading

Posted in GCMs, observations, projections, temperature, uncertainty, variability | 3 Comments

Constraining projections with observations

Can past observations be used to help constrain future temperature projections? This question is particularly relevant given the last decade which has shown relatively less warming than expected. Continue reading

Posted in GCMs, observations, projections, temperature, uncertainty | 17 Comments

Updated comparison of simulations and observations

Now that 2012 is over, it is time to update a comparison of simulations and observations of global mean temperatures.

Continue reading

Posted in GCMs, observations, projections, temperature, uncertainty | 53 Comments

What will the simulations do next?

Recent conversations on the recent slowdown in warming has inspired an animation on how models simulate this phenomenon, and what it means for the evolution of global temperatures over the next few decades. Continue reading

Posted in temperature, variability, visualisation | 26 Comments