What Will The World Actually Look Like At 1.5°C Of Warming?

What Will The World Actually Look Like At 1.5°C Of Warming?

The high ambition of the Paris Agreement, to limit global warming to “well below 2°C”, was driven by concern over long-term sea level rise. A warmer climate inevitably means melting ice – you don’t need a computer model to predict this, it is simple common sense.

As temperatures rise, sooner or later much of the world’s glaciers will become water, which will end up in the ocean. With enough warming, ice sheets could also begin to melt irreversibly. Also, water expands as it warms. Although the full impact will take a long time – centuries or more – the implications of even only 2°C warming for low-lying coastal areas and island states are profound. This is why, in Paris, the world agreed to “pursue efforts” to go further, and limit warming to 1.5°C above pre-industrial levels.

“Pre-industrial” is not always well-defined, but is often taken as 1850-1900 since that is when accurate measurements became widespread enough to estimate global temperature change. By the 1980s, when scientists first warned about the risks of climate change, the world had already warmed by around 0.4°C. Things have accelerated since, and while year-to-year changes show downs as well as ups, the general ongoing trend is upwards. Latest data from the Met Office shows 2016 is expected to be 1.2°C above pre-industrial levels – the hottest year ever recorded.

So given this, what will a world above 1.5°C look like?

Not much different … at first

Depending on climate sensitivity and natural variability, we could conceivably see the first year above 1.5°C as early as the late 2020s – but it is more likely to be later. In any case, the first year above 1.5°C above pre-industrial temperatures will not represent what a world that warm looks like in the longer term.

During that year we’d expect some extreme weather events somewhere in the world, as happens every year. Some of these heatwaves, heavy downpours or droughts may well have become more likely as part of the changing climate. Others, however, may not have changed in likelihood. Teasing out the signal of climate change from the noise of natural variability is hard work.

But there will be some places which do not yet see major impacts in that first year, that nevertheless will have become more likely to be affected. The “loaded dice” analogy is rather clichéd, but nevertheless useful – even a pair of loaded dice will not roll a double six every time, just more often than normal dice. So while the chances of an extreme heatwave, for instance, may have increased by the time we exceed 1.5°C, it may not necessarily occur in that year.

Furthermore, some impacts such as sea level rise or species extinctions will lag behind the change in climate, simply because the processes involved can be slow. It takes decades or more to melt glaciers, so the input of extra water to the oceans will take time.

None of this should lull us into a false sense of security, however. While rising seas or biodiversity losses may not be obvious in the first year above 1.5°C, some of these changes will probably be already locked in and unavoidable.

Beyond global warming

The impacts of increased carbon dioxide do not just come from its effects as a greenhouse gas. It also affects plant growth directly by enhancing photosynthesis (“CO₂ fertilisation”), and makes the sea less alkaline and more acidic. “Ocean acidification” is unhealthy for organisms which make calcium in their bodies, like corals and some forms of plankton. All other things being equal, CO₂ fertilisation could be viewed to some extent as “good news” as it could help improve crop yields, but even so, the implications for biodiversity may not all be positive – research has already shown that higher CO₂ benefits faster-growing species such as lianas, which compete with trees, so the makeup of ecosystems can change.

The extent to which a 1.5°C world will see these other impacts depends on the still-uncertain level of “climate sensitivity” – how much warming occurs for a given increase in carbon dioxide. Higher sensitivity would mean even a small rise in CO₂ would lead to 1.5°C, so fertilisation and acidification would be relatively less important, and vice versa.

Impacts of staying at 1.5°C

There is a huge debate about whether limiting warming to 1.5°C is even possible or not. But even if it is, limiting global warming will itself have consequences. I’m not talking here about potential economic impacts (whether positive or negative). I’m talking about impacts on the kind of thing we are trying to protect by minimising climate change itself, things like biodiversity and food production.

In scenarios that limit warming at 1.5°C, net CO₂ emissions would have to become negative well before the end of the century. This would mean not only stopping the emission of CO₂ into the atmosphere, but also taking huge quantities of it out. Large areas of new forest and/or large plantations of bioenergy crops would have to be grown, coupled with carbon capture and storage. This will require land. But we also need land for food, and also value biodiverse wilderness. There is only so much land to go round, so difficult choices may be ahead.

So while the Paris Agreement ramped up the ambition and committed the world to trying to limit warming to 1.5°C, we should remember that there is much more than a single number that is important here.

It would be naive to look at the climate in the first 1.5°C year and say “Okay, that’s not so bad, maybe we can relax and let the warming continue”. It’s vital to remember that at any given level of global warming, we have not yet seen the full impacts of it. But nor have we seen the impacts of holding back warming at low levels. One way or another, ultimately the world is going to be a very different place.

The Conversation

About The Author

Richard Betts, Chair in Climate Impacts, University of Exeter

This article was originally published on The Conversation. Read the original article.

Related Books

List Price: $27.00
Sale Price: $27.00 $16.20 You save: $10.80


List Price: $23.00
Sale Price: $23.00 $17.41 You save: $5.59


List Price: $21.99
Sale Price: $21.99 $14.95 You save: $7.04


enafarzh-CNzh-TWnltlfrdehiiditjakomsfaptruesswsvthtrurvi

LATEST VIDEOS

Blue Ocean Event : Game Over?
by Just Have a Think
A Blue Ocean Event, or Ice-Free Arctic, is the source of almost fever pitch speculation in the climate science world.…
Climate Change - The Facts by Sir David Attenborough
by David Attenborough, BBC
After one of the hottest years on record, Sir David Attenborough looks at the science of climate change and potential…
Why it’s time to think about human extinction
by Kerwin Rae
After listening to this ep with Dr David Suzuki, you’ll never be the same again. The environmentalist, activist,…
Record Temperatures 20-25C Above Norm in far North
by Paul Beckwith
The Northwest Territories of Canada had March temperatures above 20C for the first time (hit 21.6C or 71F); breaking…
Why New CO₂ Capture Technology Is Not The Magic Bullet Against Climate Change
Why New CO₂ Capture Technology Is Not The Magic Bullet Against Climate Change
by Chris Hawes
According to a recent major UN report, if we are to limit temperature rise to 1.5 °C and prevent the most catastrophic…
Why Climate Change Will Dull Autumn Leaf Displays
Why Climate Change Will Dull Autumn Leaf Displays
by Matthew Brookhouse
Every autumn we are treated to one of nature’s finest seasonal annual transitions: leaf colour change and fall.
Climate denial isn’t stopping climate action.
by David Wallace-Wells
Climate change denial draws headlines. But is it actually an obstacle to climate action? A great majority of Americans…
Energy Storage: How to store renewable energy?
by Total
Under your bed, in the attic even on your mobile phone, it seems there's never enough storage. It turns out it's also…

LATEST ARTICLES

Crops at risk from changing climate
Crops at risk from changing climate
by Tim Radford
Global warming could bring yet more challenges to a hungry world. New studies have identified precise ways in which a…
Seeing The Planet Break Down In Climate Crisis Is Depressing – How To Turn Your Pain Into Action
Seeing The Planet In Climate Crisis Is Depressing – Turn Your Pain Into Action
by Cameron Brick
Environmentalism can feel like a drag. People trying to reduce their environmental impact often feel stressed and…
Global Inequality Is 25% Higher Than It Would Have Been In A Climate-stable World
by Nicholas Beuret
Those least responsible for global warming will suffer the most. Poorer countries – those that have contributed far…
Jason Kenney's Victory Means We'll All Pay The Price For Fossil Fuel Emissions
Jason Kenney's Victory In Alberta Means We'll All Pay The Price For Fossil Fuel Emissions
by D.T. Cochrane
Jason Kenney has led the United Conservative Party to victory in Alberta. There were manyobjectionablecomponents to the…
How Can Trees Really Cool Our Cities Down?
How Can Trees Really Cool Our Cities Down?
by Roland Ennos, University of Hull
In cities around the world, trees are often planted to help control temperatures and mitigate the effects of the “urban…
Beto O’Rourke Releases $5 Trillion Climate Change Proposal
Beto O’Rourke Releases $5 Trillion Climate Change Proposal
by Global Warming & Climate Change
But Varshini Prakash, executive director of the Sunrise Movement, a youth-led activist group that has advocated for the…
Should The Sahara Desert Be Turned Into A Huge Solar Farm?
Should The Sahara Desert Be Turned Into A Huge Solar Farm?
by Amin Al-Habaibeh
Whenever I visit the Sahara I am struck by how sunny and hot it is and how clear the sky can be.
How Retreating From The Sea Level Rise Will Affect Our Health?
How Retreating From The Sea Level Rise Will Affect Our Health?
by Jackson Holtz
Managed retreat in the face of sea level rise will be a mixed bag, researchers predict.