Nick Breeze - Articles
- Published: 22 December 2015 22 December 2015
In the following excerpts from the conversation with Box, we discuss the cold freshwater “blob” that has appeared in the north Atlantic that could have impacts for places like the UK in terms of increased rainfall.
These feedback effects from the warming of the atmosphere could cause the Greenland ice sheet to slump in on it self and lose height. Once this happens, the surface of the ice sheet will be at a warmer altitude and the melt out will accelerate. If we get to this point it really could spell disaster for low-lying coastal areas around the world.
He goes on to link these effects to what is happening in Antarctica where the potential for sea-level rise impact is far greater than Greenland. Box states, “That’s the big one right?”
Box also highlights the crystal clear link between climate science and emissions policymaking, pointing out that if we stay on the business as usual (BAU) path of continued and increasing emissions of CO2 and other greenhouse gases, then the atmosphere will continue to warm and the demise of the ice sheets will happen faster.
If we can implement ambitious emissions cuts and curb our CO2 pollution then we could slow that melt out of Greenland and Antarctica ice sheets. The window for this is closing but we can be hopeful that if we do the right thing now concerning mitigating the effects of climate change, then we can make a real difference.
We have just had extreme rainfall in the UK that has resulted in loss of life and enormous damage to property. We know that these events are going to rise, but are there any links between this kind of event and the melt out of the Greenland ice sheet into the North Atlantic?
Jason Box: We connected the possibility Greenland melting with this cold blob in the north Atlantic. At the same time the surface air temperatures are at a record high, surface sea temperatures are at a record low and its a very conspicuous feature of the global temperature map. Why is there this cold blob?
What we know is that there is a capacity for some recirculation of accumulated melt water to come from Greenland melting and then that cold pool can strengthen storms when the sea temperatures to the south are normal. So if you have normally warm temperatures here and abnormally warm temperatures here, this can strengthen storms.
So the fact that Iceland had a terrible storm just 3 days ago, and the fact that the UK, 2 days before that had a terrible storm, record setting storm, it is part of a pattern that could be part of this cold pool, this so called “cold blob” in the north Atlantic. And the science is starting to come out on that topic, that it appears that this cold blob is producing stronger storms, and that Greenland melting could be part of that.
So Greenland’s got its impacts on sea level, this cold blob, and also changing nutrients applied to the surrounding oceans, which could affect fisheries. We don’t know whether that is a positive or negative at the moment for fisheries but there is more sedimentation coming out of the Greenland ice sheet.
Nick Breeze: Is there a change in the salinity of the water?
Jason Box: The surface salinity in the north Atlantic is lower, the salty warm water that is coming up is part of the gulf stream.
Antarctica, expanding sea ice, because Antarctica is a net loser of ice, this has a potential to freshen the surface layers of the waters around Antarctica as well, and that can cap the radiative cooling of the southern oceans and that could produce an accumulation of heat in the vicinity of the Antarctic ice sheet.
So if that increasing warm pool that is being capped by the fresh water layer in the southern oceans, that is threatening to erode the Antarctic ice sheet… that is an example of a feedback mechanism that is not in the climate models that could lead to a faster loss of the Antarctic ice sheet. That’s the big one right? That’s the one that’s going to produce a lot more sea-level rise than Greenland is going to.
Nick Breeze: And that is global right? We tend to think of things in terms of northern hemisphere, mid attitudes and southern hemisphere, but it’s a global system?
Jason Box: Yeah, it is really important, you know, I am like a “Greenlandist” but Antarctica matters more if it takes over. Greenland has been providing more than a factor of 2 to sea-level than Antarctica in the last 20 years. But Antarctica has the capacity to take over. I suppose it will in the coming decades.
Then Antarctica has the potential to overwhelm sea-level rise because it is nine times the volume of Greenland. This mechanism of fresh water capping the southern oceans radiative cooling, accumulation of heat in the vicinity of the Antarctic, is concerning to me!
If the surface water [in the southern oceans] is being capped by freshwater and shutting off that normal heat release by radiation to space, that’s a big deal, if that is happening.
Nick Breeze: When you are talking about the general temperature rising, which causes more melt, the melt is on the surface but the dynamics of the ice sheet, as I’ve read, is that there is a lot going on inside the ice sheet, it’s not all on the surface?
Jason Box: It’s interesting to follow the water, as it is produced on the surface, or even arrives on the surface in the form of rainfall. In some heavy rain instances, the water drains down in, being at a higher temperature than the ice itself, the water, whether it is melt water or rainwater, has the capacity to heat the ice internally and warmer ice is softer, it flows faster, the water then continues to the bed where it is either stored or transmitted. Under some conditions it can lubricate flow.
During heavy rain periods you can get accelerated flow, that can produce some gliding effects, then the water comes out the front, and if that is in a marine environment, it forces a heat exchange between ocean waters. If that is deep enough, below about 350metres, that can be a much more efficient way to transfer heat from this relatively warm Atlantic water layer. This is only important for the deepest, thickest glaciers, and that is eroding ice at the grounding line.
So that is an important connection between surface melting flow through the ice and a forced heat exchange, under water at the deepest glacier fronts. That is a destabilising effect.
Nick Breeze: Obviously, it is so vast, the Greenland ice sheet, is it something causing enormous concern, or something you are monitoring?
Jason Box: If climate continues warming, a number of processes start to multiply. That is increasing snow line, that is exposing a larger area of darkness, the bare ice area is darker than the snow cover. Another is a longer season of how long ice algae can colonise and grow and get darker. There is more liquid water in a warmer climate on the surface, the ice lakes forming higher, and the possible factor of wildfire. We think that wildfire is increasing with climate warming. The numbers are pretty noisy, so it is hard to say that for sure, for sure, but we think think wildfires are increasing with climate warming.
Nick Breeze: We are seeing wildfires all over the planet aren’t we?
Jason Box: Yes, so the question is, is that increasing? There is some evidence in North America of an increase in wildfire, so connecting that with Greenland ice, we need better measurements of black carbon, we need more measurements.
Nick Breeze: So you need more resources?
Jason Box: Yeah, we’ve made a handful of black carbon measurements, it’s not enough to be conclusive but what I feel confident about is that black carbon does provide heating of snow and ice surfaces and that can, all else equal, give an earlier melt onset, and expand the melt season that way.
The climate science is the underlying basis for assessing the threats, the risk of climate change. In the work that you are doing, are their risks relevant to what we are trying to stave off, such as a fully destabilised ice sheet?
The Greenland ice sheet, like any land based ice mass is a threshold system. In the current climate, Greenland is beyond it’s threshold. However, it is not losing ice catastrophically, We are about 1.2 Celsius above preindustrial temperatures for Greenland in summer. The threshold viability, the best guess has been put at 1.65 Celsius, but it is just in a zone where it is losing mass. That has been confirmed with multiple independent lines of measurements.
The real point is how far beyond that threshold do we push this ice sheet? Do we push it to a 2ºC, a 4ºC summer warming? The two scenarios, the BAU scenario will have Greenland warming in summer by about the end of century by about 6ªC .
Then in the carbon mitigation scenario is about half as much. So it’s about 3 Celsius, in summer. It’s not losing ice super fast. It’s losing about 300Gt’s, just under 3mm per year.
Nick Breeze: You were talking earlier about the insides of the ice sheet changing. Can this cause a non-linear effect?
Jason Box: There must be non-linear effects. We actually see the shape of the ice loss appears to be non-linear. What’s really important though, if we could simplify as much as just looking at temperature, as temperature rises, the rate probably increases, probably non-linearly.
So, if we have a climate change scenario with a plus 3 Celsius summer temperature increase in Greenland, that’s much lower than, in a carbon regulation scenario, than in a business as usual scenario. In other words, mitigation matters!
is there this threshold that we can go beyond and the mechanics of the ice sheet change and then we are stuck in this scenario where we are going to get the sea-level rise?
The key irreversibility for Greenland has to do with its elevation and if dynamic thinning can produce enough drawdown of the surface elevation to warmer parts of the atmosphere, if there is enough slumping, then we cannot recover without cooling several degrees.
But where we are today, we are not beyond that threshold, we are not at the point of irreversibility. We are moving in that direction and even in an optimistic climate mitigation scenario, we are still moving in that direction. So, it’s alarming. The message for decision makers should be, we need to stay down below 2ºC, say below 1.5ºC, and more importantly, devise technologies to remove carbon from the atmosphere, drawdown.
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