How much the planet warms for each tonne of carbon dioxide is still one of the biggest questions in climate science and uncertainty in that response makes it harder to set clear emission targets.
Now a team of researchers in Japan has combined climate model projections with real world observations to sharpen estimates of future warming and the remaining carbon budget for limiting temperature rise to 2°C.
The study uses results from 20 state of the art Earth system models that took part in the CMIP5 and CMIP6 exercises underpinning recent IPCC reports.
The team examined not only how these models react to rising carbon dioxide concentrations, but also how human emissions translate into atmospheric levels through the carbon cycle, as forests, soils and oceans absorb part of what we emit.
They found many models warm the planet too quickly for the amount of carbon released so far. By giving greater weight to models that better match observed temperature and carbon dioxide trends, the researchers narrowed the spread of 21st century warming outcomes and refined the remaining carbon budget.
Previous studies that did not account for agreement with observations put the remaining 2°C budget at about 352 billion tonnes of carbon, with a vast range from 2 to 702 billion.
The new analysis revises the mean to 459 billion tonnes but with a tighter range of 251 to 666 billion, improving confidence in the figures.
The work also shows how differences in the “airborne fraction” of emissions and the split between land and ocean sinks can drive divergent projections.
For policymakers the message is clear: the science behind carbon budgets is getting more precise – but at current emissions of around 11 billion tonnes of carbon a year the 2°C budget will still be used up within a few decades without rapid cuts.
New science tightens estimates of 2°C carbon budget appeared first on Energy Live News.