The study, which was organised by the World Climate Research Programme (WCRP) and involving many leading climate scientists (including one of us: Tim), looks at a measure called “equilibrium climate sensitivity”. This refers to how much global average temperatures will increase by in the long-term following a doubling of carbon dioxide concentrations. It can be estimated using three main lines of evidence:
- Temperature measurements made with thermometers from 1850 (when enough global coverage began) to the near present. By comparing temperatures, CO₂ levels and the effect of other climate drivers in the past and present, we can estimate the longer-term changes.
- Evidence from paleoclimate records from the peak of the last ice age 20,000 years ago, when CO₂ was lower than now, and a warm period around 4 million years ago when CO₂ was more comparable to today. We can tell how warm the climate was and how much CO₂ there was in the atmosphere based on the make-up of gases trapped in air bubbles in ancient ice cores.
- Present-day observations – for instance from satellite data – and evidence from climate models, theory and detailed process models that examine the physics of interactions within the climate system.
Despite its importance, equilibrium climate sensitivity is very uncertain and for many years the standard estimate has been 1.5°C to 4.5°C. In its 5th Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) gave these values as the “likely range”, which meant it considered there was at least a 66% chance that it fell within this range. Or, in other words, it judged there was up to a 33% chance that warming would either be less than 1.5°C or more than 4.5°C.
Coronavirus is an extra setback for island states already suffering from climate change and storms such as Cyclone Harold and Hurricane Dorian. They are also preparing for the next season… What are the implications for the efficacy of coronavirus measures as well as for the economic resources available to respond to the pandemic?
This blog post by Adelle Thomas, Climate Analytics Senior Caribbean Research Associate and CONSTRAIN Stakeholder Committee Member, explains how these compound risks underscore the extreme vulnerability of SIDS, and the need for an international response that helps us all to avoid dangerous climate change.
Hurricane Dorian damage in the Bahamas ©Coast Guard News