Reconstructing Atlantic atmospheric variability

Posted on February 8, 2012 by Ed Hawkins

In a previous post I discussed the Old Weather project which is using volunteers to transcribe the hand-written weather data from Royal Navy ships logs in the World War 1 period. The good news is the first 243 ships have been completed (providing data scattered throughout the period 1914-1923), and some simple analysis shows whether this data can help reconstruct past Atlantic atmospheric variability. Continue reading →

Posted in Atlantic, history, variability, weather | 3 Comments

The importance of reliable uncertainty estimates

Posted on January 3, 2012 by Ed Hawkins

Reliable estimates of uncertainty are arguably more important than the actual value being quoted. I recently came across a classic example in astronomy. Continue reading →

Posted in uncertainty | 14 Comments

What happens if you spin the Earth backwards?

Posted on December 8, 2011 by Robin Smith

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. Continue reading →

Posted in GCMs, MOC | 11 Comments

Time of emergence of climate signals

Posted on December 5, 2011 by Ed Hawkins

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. Continue reading →

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

Uncertainty in temperature variability

Posted on November 13, 2011 by Ed Hawkins

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. Continue reading →

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

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

Posted on September 27, 2011 by Ed Hawkins

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 it is changed to “when will it happen”? Continue reading →

Posted in GCMs, projections, temperature, uncertainty | 7 Comments

Uncertainty in uncertainty

Posted on August 24, 2011 by Ed Hawkins

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? Continue reading →

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

Trends in Central England Temperature

Posted on August 10, 2011 by Ed Hawkins

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. Continue reading →

Posted in GCMs, temperature, variability | 4 Comments

Visualising climate with 2d colour bars

Posted on July 10, 2011 by Ed Hawkins

A recent paper by Teuling et al. suggested the use of 2d colour bars for visualising climate fields. I thought I would give this a try – and Ryan Teuling was kind enough to provide the code to construct the colour bars. Continue reading →

Posted in precipitation, projections, uncertainty, visualisation | 1 Comment

Learning about past climate from ships logs

Posted on June 17, 2011 by Ed Hawkins

Understanding the climate of the past is extremely valuable to help put modern weather observations into a long-term context. Although we have considerable records of past weather, especially over land, more data is always welcome. Given the British obsession with the weather it is perhaps of no surprise that more data is available, it is just buried in hand-written logbooks. Transcribing this data is normally a time-consuming and expensive task…. Continue reading →

Posted in Arctic, history, sea-ice, variability, weather | Leave a comment

When to use uncertain climate forecasts

Posted on May 12, 2011 by Ed Hawkins

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 projected change to the spread around that change. An important question is ‘when does the spread in the forecasts become so large that the forecast should not be used’? Continue reading →

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

What is a year?

Posted on March 17, 2011 by Ed Hawkins

A rather surprising question perhaps, but the answer is, ‘it depends’. There is no climatic reason to define a year from January to December, but that is what is generally done. But, is this the best definition? Continue reading →

Posted in SSTs, temperature, variability | 3 Comments

Hysteresis of the Atlantic MOC in an AOGCM

Posted on March 10, 2011 by Ed Hawkins

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 that the density driven circulation in the Atlantic Ocean has two equilibrium states, either ‘on’ or ‘off’. If the climate is altered, a transition may occur between these states which is not reversible by returning the climate to its previous regime (this irreversibility is termed ‘hysteresis‘). Continue reading →

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

Arctic predictability

Posted on November 1, 2010 by Ed Hawkins

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

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

A brief history of early climate science

Posted on August 23, 2010 by Ed Hawkins

Something a little bit different for this post…. After all the recent controversy over hacked emails, IPCC errors and the British public apparently growing more skeptical about climate science and scientists, it is perhaps interesting to take a step back and look at why we believe that emissions of various gases can influence our climate. Continue reading →

Posted in history | Leave a comment

Atlantic multi-decadal variability

Posted on August 20, 2010 by Ed Hawkins

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’. Continue reading →

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

Communicating climate variability

Posted on August 11, 2010 by Ed Hawkins

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. Continue reading →

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

Consensus in precipitation projections

Posted on June 25, 2010 by Ed Hawkins

In the AR4, the IPCC presented this figure showing the consensus in precipitation projections for the 21st century, designed to be of use to planning for adaptation and mitigation. The coloured regions show where changes are likely to occur. My interest is in the white areas where models cannot agree on the sign of the change. This could mean that half the models predict a large drying and half predict a large increase in rainfall. But, it could also just mean that the changes are small, but that the sign is uncertain. Continue reading →

Posted in GCMs, precipitation, projections, variability | 2 Comments

Global mean temperature variability in observations and GCMs

Posted on June 24, 2010 by Ed Hawkins

I am often surprised at how different climate models can be. Shown below is the annual mean, global mean surface air temperature from control runs of 21 of the AR4 GCMs, along with the observations (HadCRUT3). Continue reading →

Posted in GCMs, temperature, variability | Leave a comment