Arctic sea-ice decline erratic as expected

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. Continue reading Arctic sea-ice decline erratic as expected

Is there a pause in the temperature of the lower troposphere?

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.

Guest post by Geert Jan van Oldenborgh, KNMI Continue reading Is there a pause in the temperature of the lower troposphere?

Projected changes of precipitation and temperature extremes

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

The slowdown zoo

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

Earth’s energy imbalance

Global surface air temperatures have risen less rapidly over the past 15 years than the previous few decades. The causes of this ‘hiatus’ have been much debated. However, just considering surface temperatures does not tell the whole story – a new analysis using satellite & ocean observations confirms that the Earth is still gaining energy overall. Continue reading Earth’s energy imbalance

Wet get drier (eventually)?

A prevailing paradigm of how rainfall patterns will change on a warming Earth is that the hydrological cycle strengthens causing wet regions to get wetter and dry regions to get drier.

However, this is not always the case: Hawkins, Joshi & Frame (2014) highlight one particular effect – the movement of the Inter-Tropical Convergence Zone (ITCZ) – as a key long-term driver of rainfall changes that do not follow this ‘wet get wetter’ paradigm. Continue reading Wet get drier (eventually)?

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

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 Getting a Comment published in Nature

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 On Mora et al.’s Reply

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 Uncertainties in the timing of unprecedented climates

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 The signal, the noise & the time of emergence

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 Improving the weather from 96 years ago

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 Predictable September Arctic sea-ice minimum?

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 When will we reach 2°C?

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 Comments on the GWPF climate sensitivity report

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 The cascade of uncertainty in climate projections

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 Atlantic overturning in decline?

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 Updates to comparison of CMIP5 models & observations

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 Effects of recent observed vs RCP forcings

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 Sources of uncertainty in CMIP5 projections

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 Time of emergence of a warming signal

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