Today an international group of hundreds of climate scientists released a report covering how and why the earth’s climate is changing, and how it may change in the future.
Scientists are 95 per cent confident that humans are changing the climate
The topline from the new report – and one many media outlets have picked up on – is that scientists can now say with extremely high confidence the world is warming and that humans have been the dominant cause of that warming since the 1950s.
Dr John King from the British Antarctic Survey tells us:
“[T]he message I would want people to take home is increasing certainty that human activity has been having an impact on climate and will continue to do so into the future, that we are now able to make predictions with increased confidence”
King adds a note about how confidence in this message has grown stronger in recent times, saying:
“I think it’s interesting to look at this in the context of the whole series of IPCC assessments that have come out. We’re now on the fifth one and over time the message that has become stronger and stronger that there is a measurable human impact on climate …The message hasn’t changed, it’s just being delivered with greater and greater confidence as the evidence base has accumulated”
Dr Matt Collins from the Met Office echoes this point, telling us:
“[In this report] the observations are longer, they’re showing us the signal we expected them to show, some of the attribution statements are stronger, we better understand aspects of the way the future projections work. Really, this is a reaffirmation of the findings from the last assessment report, with a strengthening of the many lines of evidence.”
And Professor Rowan Sutton from the University of Reading, tells us:
“I think the report is very clear and the evidence is very strong â?¦[It] reinforces what we concluded in previous assessment reports that the evidence [for a human contribution to warming] is that much stronger and leaves no room for doubt whatsoever.”
Warming of the climate system is unequivocal, and there are many ways to measure it
The report is crystal clear on the importance of looking at the climate system as a whole, not focusing on one measure of climate change in isolation. There are many lines of evidence for the impact humans are having.
According to Dr Kate Willett from the Met Office:
“Traditionally, we always see surface temperature as our key metric of climate change â?¦ [This report] includes a greater understanding of the climate system as a whole and the realisation that its not just about surface temperature, there are so many other metrics that show evidence of change â?¦ This report does paint a more complete picture than ever before.”
The Met Office’s Dr Peter Stott echoes this point, telling us:
“The great majority of the energy imbalance in the climate system has been warming up the ocean. But of course it’s also been melting snow and ice and it’s been warming up the surface of the earth.”
Rowan Sutton tells us the emphasis on the climate system as a whole “reflects how the science has moved on”. He says:
“[E]arly studies focused mainly on surface temperature but in recent years similar approaches have been applied to understand changes in many other aspects of the climate system. It’s really the consistency we see across these different aspects that gives us such high confidence that human activities are having the strong impact that they are.”
The IPCC: A bridge between science and policy
Distilling thousands of pages into a 30-page synthesis is hard enough. A major additional challenge in producing the Summary for Policymakers is that it needs to reflect the complexity of the science while at the same time being understandable to policymakers.
Kate Willett tells us she’s confident the report succeeds in both. She says:
“I do think we’ve done a good job [in producing this report] I don’t know what that means for the future, whether this is the right format or not â?¦ But I’ve been really pleased with the process from the start, it’s been as transparent as it can be.”
John King adds:
“The report is a great achievement. It provides this huge collection of scientific evidence. It was commissioned by governments worldwide, it’s now up to those governments to take it, to look at what the science is saying, and to think about how policy should be developed that reflects what that science says.”
A carbon budget for the future
Now that the scientific statements are out there, what happens now? Sutton explains that the new report gives some very clear guidelines for what global governments need to do to steer clear of two degrees of warming above pre-industrial levels, the internationally accepted target to avoid dangerous climate change.
Rowan Sutton tells us:
“In terms of the risk for the future … the report makes the very clear statement that there’s a very substantial risk of exceeding two degrees, only under a very ambitious scenario for reducing emissions is it considered unlikely that we would cross two degrees by 2100. This is a sobering message and highlights the reality that we are facing very significant risks if we continue to emit greenhouse gases at current rates.”
For the first time, the IPCC has laid out a ‘budget’ for human emissions, starting from the beginning of the industrial era, that we’ll have to respect in order to limit temperature rise to two degrees above pre-industrial levels.
The report says that to have a 66 per cent chance of staying within that budget, humans can only emit 1000 billion tonnes of carbon. By 2011, more than 500 billion tonnes of carbon had already been released – so about the budget has already been spent.
And that budget is even tighter when you include other factors that warm the climate system. Matt Collins tells us:
“If you take into account other greenhouse gases, that target is now down to 800 billion tonnes of carbon. So really we’re nearly two thirds of the way to two degrees warming, not half way â?¦There are still remaining uncertainties in some aspect of the science, but the weight of evidence is enough to justify action.”
On the urgency of the message, Rowan Sutton is also clear:
“This is a key message for governments and a it can’t be repeated too often that the climate system only responds slowly to changes in emissions – on timescales of decades – so it’s crucial we take decisions sooner and not think we can postpone these decisions and load them onto the next generation.”
We’ll have more reaction from scientists next week.