A major UN report dubbed a "survival guide for humanity" this week said the Earth would reach 1.5 degrees of warming by the early 2030s unless deep and rapid action is taken to slash emissions across all sectors. RFI spoke with Gerhard Krinner, head of CNRS research at France's Institute of Environmental Geosciences, who is also a main author of the IPCC's definitive report on climate change this decade.
RFI: The AR6 Synthesis Report has been called the "report of reports", condensing six years of work. It's meant to inform policymakers at Cop28 in November and in the years beyond. Have we reached a point where there's enough science: we know the tipping points are there; we know what the consequences of uncapped warming will be ... and so only action matters now?
GK: We've known what will happen for decades. The first IPCC report made the projections of climate change that have become a reality today.
In that sense, the essential information has been out in the world for 30 years, but there are a lot of details that we still don't know. For example, you mentioned tipping points.
A tipping point is when something happens in the climate system suddenly and irreversibly because a threshold has been crossed. We do not know where all the tipping points are. There are a lot of tipping points in the climate system.
For the West Antarctic ice sheet, we know that at some level of temperature there will be processes kicking in that will lead to its disintegration. However we don't know exactly where these are and at what scale.
There's a lot of research still needed about tipping points, but what we do know is that the warmer it gets in the world, the higher the probability that we will cross them.
RFI: The report tells us that the longer we wait, the harder it's going to be to adapt to climate change. Could you explain in which ways that challenge is becoming bigger and bigger and ultimately insurmountable?
GK: The essential message concerning 1.5 degrees is that it's not a cliff we will be falling over. It's like more like a slippery slope that is getting steeper and steeper the higher we get in terms of climate warming.
Already, today, we are unable to adapt to all the effects of climate change in every region.
Climate change has different impacts in different regions of the world, and specifically in the regions that have not contributed a lot to climate change.
Today we are progressively reaching points where adaptation will no longer be possible for ecosystems and also for human systems.
This means the options we have to adapt to climate change and to mitigate it are becoming more and more constrained. If you want to adapt your agriculture to a changing climate, for example, it's getting more and more difficult.
RFI: We're told that every fraction of a degree of warming matters. There's growing recognition that 2 degrees of warming is dangerous. Remind us just how dangerous, and how a world of 2 degrees warming compares to one of 1.5?
GK: It all depends on the time scale you're looking at. For example, 2 degrees of warming on a very long time scale means you would see two to six metres of sea level rise. That is enormous, but it's simply linked to the long time it takes for the ice sheets to melt.
So over the long term 2 degrees is really a very different world compared to 1.5 degrees.
The assessment published a few years ago in the special report on 1.5 degrees warming clearly showed there are discernible differences in the frequency of heatwaves and strong precipitation events in many regions between 1.5 and 2 degrees.
The changes in extreme weather events in particular is very significant between 1.5 and 2 degrees.
RFI: We've got more or less 10 years to adapt before the world hits 1.5. Europe is warming twice as fast as the rest of the world. What happens in a place like Europe once we we hit 1.5 and beyond?
GK: The question really is are we going to just hit 1.5, or are we going to run through it and go on to 2 degrees and 2.5 and 3 degrees?
Looking at what policies have been implemented, we're on track for 3 degrees in 2100, and Europe is one of the regions where climate change is particularly strong.
I live in Grenoble. When I moved here 30 years ago I saw a small glacier from from the city. It's not there anymore. So the glaciers in the Alps close to us are going to melt away very soon. At the end of the century they won't be there anymore.
This will impact water availability in regions where fresh water resources are dependent on glaciers.
While that's not very often the case in Europe, we know the Mediterranean region and southern Europe will be very much impacted by a decrease in precipitation (rain).
There's also the risk of inundations (floods) due to increases of extreme precipitation, even in regions where mean precipitation decreases and there are more and more heatwaves.
RFI: We know that warmer temperatures have been more widespread across the Northern Hemisphere since the mid 20th century than in any other time. We know that solar and volcanic activities have played a role over the past thousand years. But how do we know this unprecedented warmth is directly linked to emissions caused by humans?
GK: That is what we call the science of attribution. How do we know what the reason is for the climate change we are observing now? Climate change has a temporal and a spatial pattern.
As you say, warming is stronger in the Northern Hemisphere than in the Southern Hemisphere. It's also clear there is warming in the troposphere and cooling in the stratosphere.
So what is the stratosphere? That's the upper part of the atmosphere beyond 10 kilometres and up to about 50 or so, and it's cooling. We know that greenhouse gases have the effect of warming in the lower part of the atmosphere, and cooling in the upper part of the atmosphere.
That is the fingerprint of the greenhouse effect. If the sun had been causing the warming, we would not have that vertical structure. The fingerprint would be very different.
By comparing the spatial fingerprint and the temporal fingerprint, we know the effect on climate by volcanoes, the sun, greenhouse gases and so on.
This has led to the assessment that all of the observed change in global mean temperature is actually caused by human activity.
RFI: The synthesis report tells us 1.5 is still achievable if we act urgently. To reach that target no new fossil fuel resources can be opened, but countries are still exploiting traditional energy sources like coal and gas. Doesn't this alone mean we're going to fail on 1.5?
GK: The assessment is quite clear that, yes, we will certainly reach 1.5 in the first half of the 2030. But reaching 1.5 is not the end of the world. Once we have crossed the 1.5 threshold we then have to limit warming to below 1.6, or below 1.7 and so on.
There will be possibilities if, in the remainder of the century we are able to reduce our carbon emissions to zero, to return back to below 1.5.
It's extremely important to limit warming because that also limits sea level rise, and the speed of the sea level rise. When change happens too fast, you can't adapt anymore.
Adaptation measures can take a long time to plan, such as relocation. If you know your area is going to be inundated, you have to plan for relocation or building dams.
That takes a long time. If the rate of sea level rise is slower, you can do that.
RFI: If the world does introduce the transformational change needed to bring down emissions, how long must we wait before we see a change in temperature trends?
GK: There is interannual variability in temperature. Some years are warmer and others are colder. In 2030, for example, there is already a 40 to 60 percent chance that any individual year will be above 1.5.
However if we introduce very strong, sustained CO2 reductions, compared to a pathway in which we continue increasing CO2 emissions, we would see the effect on global mean temperatures emerge very discernibly within 20 years.
It takes some time for global mean temperatures to change, but it's much faster for air quality.
RFI: Does the fact that governments have signed off on this report mean we're more likely to see meaningful action on climate at a state level, and more concrete commitments at the next Cop in Dubai?
GK: This report contains clear numbers of the required emission reductions to keep our pathway consistent with 1.5 or 2 degrees.
These are numbers given for the years 2030, 2035 and 2040. This is what's called the global stocktake within the United Nations framework on climate change, which leads to these Cops every year.
The objective of the global stocktake is to say: "Where are we? How is the climate changing? Is our action enough?" This is part of the Paris Agreement and the Synthesis Report is one basis of that. It's going to be very important.
Of course, there's some resistance against this. It's quite obvious that if you are a country exporting oil, you want to sell your oil. But most countries also have a clear interest in reducing fossil fuel emissions.
The benefit of reducing our emissions is absolutely clear.
