Category Archives: GCMs

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 … Continue reading

Posted in climate sensitivity, GCMs, IPCC AR5, observations, projections, temperature, uncertainty | 223 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 … 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 … 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 … Continue reading

Posted in GCMs, IPCC AR5, projections, temperature, uncertainty | 8 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 … Continue reading

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

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?

Posted in GCMs, observations, projections, temperature, uncertainty, variability | 6 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 … 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.

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.

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

Visualising the role of natural variability

A new analysis by Clara Deser and colleagues (accepted for Nature Climate Change), provides some fantastic visualisations of the crucial role of natural variability in how we will experience climate.

Posted in GCMs, projections, temperature, uncertainty, variability, visualisation | 17 Comments

Global temperatures over the past decade

It is well known that the past decade or so has seen less global warming than might have been expected – but what is the cause? This is more of a discussion post, rather than any new analysis.

Posted in GCMs, projections, temperature, variability | 31 Comments

Predicting changes in North Atlantic temperatures

The Earth is a complex system of interacting components, such as the atmosphere and ocean, which produce a wide variety of natural variability. This natural variability ensures that the evolution of a particular region’s climate, e.g. that of Western Europe, … Continue reading

Posted in Atlantic, GCMs, MOC, predictability, SSTs, variability | 1 Comment

On comparing models and observations

There has been some recent blog discussion on comparing observations and climate models consistently. Here is my effort at such a comparison using the CMIP5 models which are already available.

Posted in GCMs, projections, uncertainty, variability | 98 Comments

What happens if you spin the Earth backwards?

This might sound like a crazy idea, but bear with me. I mean, why not? We’ve got some pretty general computer models of the climate, all we have to do is change the sign of a couple of numbers.

Posted in GCMs, MOC | 15 Comments

Time of emergence of climate signals

The time at which the signal of climate change emerges from the ‘noise’ of natural climate variability (Time of Emergence, ToE) is a key variable for climate predictions and risk assessments.

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

Uncertainty in temperature variability

It is well known that there is considerable uncertainty in the projected response of climate models to increases in radiative forcing. However, there is also considerable uncertainty in the model simulated internal variability.

Posted in GCMs, temperature, uncertainty, variability | 1 Comment

Climate uncertainty: moving from ‘what’ to ‘when’

Update (23/10/11): The full article has now been published in Nature Climate Change Climate projections (such as from the IPCC) usually consider the question of “what will happen to our future climate”. But, this question may be more informative if … Continue reading

Posted in GCMs, projections, temperature, uncertainty | 8 Comments

Uncertainty in uncertainty

There has been much discussion recently on whether GCMs participating in intercomparisons, such as CMIP3 and CMIP5, are ‘independent’. But if they are not, how does this make a difference to the uncertainty in our projections for future climate?

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

Trends in Central England Temperature

Previous posts have discussed climate variability in general, and modelled decadal trends in temperature specifically. However, I should have considered decadal trends in observations as well, especially as there is a long temperature record available for the UK.

Posted in GCMs, temperature, variability | 5 Comments

When to use uncertain climate forecasts

Climate models produce projections of changes in climate from the present day, but these projections have a range, or spread. A simple measure of the confidence in a forecast would be the signal-to-noise ratio, r, of the size of the … Continue reading

Posted in GCMs, precipitation, projections, uncertainty | Leave a comment

Hysteresis of the Atlantic MOC in an AOGCM

UPDATE (16/06/11) – the paper describing this work has now been published and highlighted. The potential for a rapid collapse in the strength of the Atlantic overturning circulation (AMOC) has long been recognised. The pioneering work of Stommel first suggested … Continue reading

Posted in Atlantic, GCMs, hysteresis, MOC | Leave a comment

Arctic predictability

After attending a recent workshop on Arctic predictability, I thought a brief discussion on sea-ice variability and potential predictability might be of interest.

Posted in Arctic, GCMs, predictability, sea-ice, SSTs, variability | Leave a comment

Atlantic multi-decadal variability

Observations of Atlantic SSTs show significant multi-decadal variability since 1870 (see red line in figure 2 below), often termed the Atlantic Multi-Decadal Oscillation (AMO), though there is no clear evidence that it is really an ‘oscillation’.

Posted in Atlantic, GCMs, SSTs, variability | 2 Comments

Communicating climate variability

Update 10/03/11 – Accepted article also online. Comments very welcome. Communicating the differences and links between climate variability and climate change is of growing importance, and I am currently writing an article for “Weather” on this.

Posted in GCMs, projections, temperature, uncertainty, variability | Leave a comment