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 Hysteresis of the Atlantic MOC in an AOGCM
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 Atlantic multi-decadal 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. Continue reading Communicating climate variability
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 Consensus in precipitation projections
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 Global mean temperature variability in observations and GCMs