© Reuters. FILE PHOTO: A crushed bottle is seen on the dry land of the Jaguri Dam, part of the Cantarera reservoir system, during a drought in Guanopolis near Sao Paulo, Brazil October 8, 2021. REUTERS/AMANDA PERUBELLI/File Photo
By Kate Abnett
Glasgow (Reuters) – At the United Nations climate summit in Glasgow, world leaders have repeatedly stressed the need to limit global warming to 1.5 degrees Celsius.
The 2015 Paris Agreement commits countries to limit the rise in average global temperature to well below 2°C above pre-industrial levels, and aims for 1.5°C.
Crossing the 1.5°C threshold risks unleashing severe climate change impacts on people, wildlife and ecosystems, scientists said.
Preventing it requires nearly halving global carbon dioxide emissions by 2030 from 2010 levels and reducing them to net zero by 2050 — an ambitious task that COP26 scientists, financiers, negotiators and activists are discussing about how to achieve and pay for it.
But what is the difference between 1.5°C and 2°C of warming? We asked several scholars to explain:
where are we now?
Already, the global temperature has risen to about 1.1°C above pre-industrial levels. Each of the past four decades has been hotter than any since 1850.
“We haven’t seen such global warming in just a few decades,” said climate scientist Daniela Jakob at the Climate Services Center in Germany. “Half a degree means more severe weather, and it can often be more intense or extended in duration.”
Only this year, torrential rains inundated China and Western Europe, killing hundreds of people. Hundreds died when temperatures in the Pacific Northwest reached record levels. Greenland has experienced massive melting, wildfires have ravaged the Mediterranean and Siberia, and a record drought has hit parts of Brazil.
“Climate change is already affecting every inhabited region around the world,” said climate scientist Rachel Warren of the University of East Anglia.
Heat, rain and drought
Further warming to 1.5°C and beyond will exacerbate these effects.
“For every increase in global warming, changes in extremes get bigger,” said climate scientist Sonia Seneviratne at ETH in Zurich.
For example, heat waves will become more frequent and intense.
An extreme heat event that occurs once per decade in a climate without human influence could occur 4.1 times per decade at 1.5°C of warming, and 5.6 times at 2°C, according to the United Nations Climate Science Committee (IPCC).
Let the warming build up to 4°C, and an event like this could happen 9.4 times every decade.
A warmer atmosphere can also hold more moisture, resulting in heavier rainfall which increases flood risk. It also increases evaporation, which leads to more severe droughts.
Ice (NYSE: :), sea, coral
The difference between 1.5°C and 2°C is critical to Earth’s oceans and frigid regions.
“At 1.5 degrees Celsius, there is a good chance that we can prevent most of the Greenland and West Antarctic ice sheet from breaking,” said climate scientist Michael Mann at Penn State University.
This will help limit sea-level rise to a few feet by the end of the century – a major change that will erode coastlines and inundate some small island states and coastal cities.
But Mann said blows above 2 degrees Celsius could collapse the ice sheets, with sea levels rising up to 10 meters (30 feet) – although how quickly that could happen is uncertain.
Warming of 1.5°C would destroy at least 70% of corals, but at 2°C more than 99% would be lost. This will destroy fish habitats and the communities that depend on coral reefs for their food and livelihoods.
Food, forests, disease
Warming of 2°C, versus 1.5°C, will increase the impact on food production.
“If you have crop failures in two of the world’s breadbaskets at the same time, you can see skyrocketing food prices, hunger and starvation across large swathes of the world,” said climate scientist Simon Lewis of University College London.
A warmer world could see mosquitoes that carry diseases such as malaria and dengue spread more widely. But two degrees Celsius would also see a greater share of insects and animals lose most of their habitat, compared to 1.5 degrees Celsius, and increase the risk of wildfires – another danger to wildlife.
As the world warms, the risk of the planet reaching “tipping points” increases, where Earth systems cross a threshold that leads to irreversible or cascading effects. Exactly when these points will be reached is uncertain.
Drought, reduced rainfall, and the ongoing destruction of the Amazon rainforest (NASDAQ 🙂 through deforestation, for example, can lead to the collapse of the rainforest system, releasing carbon dioxide into the atmosphere rather than storing it. Or a warming Arctic permafrost could decompose long-frozen biomass, releasing massive amounts of carbon emissions.
“That’s why it’s so dangerous to continue emitting from fossil fuels… because we increase the likelihood that we will pass one of these tipping points,” Lewis said.
Beyond 2 degrees Celsius
So far, the climate pledges that countries have made to the United Nations Register of Pledges put the world on track for a warming of 2.7°C. The International Energy Agency said Thursday https://www.reuters.com/business/cop/net-zero-methane-pledges-push-world-near-paris-climate-goal-iea-2021-11-04 that new promises have been announced. At the top of COP26 – if implemented – it could reduce warming to less than 1.8 degrees Celsius, although some experts have challenged this calculation. It remains to be seen whether those promises will translate into action in the real world.
Warming of 2.7°C would provide “unlivable heat” for parts of the year across regions of the tropics and subtropics. Scientists said biodiversity would be massively depleted, food security would decline, and severe weather would outstrip the ability of most urban infrastructure to adapt.
“If we can keep the temperature rise below 3°C, we will likely remain within our adaptive capacity as a civilization, but at 2.7°C we will face great difficulties,” Mann said.