When the Earth was last 4 degrees warmer, approximately 25 million years ago, there was no ice at either pole. Global warming of this magnitude would eventually leave the whole planet without ice for the first time in 40 million years, leading to sea rises of 50 to 70 meters.
Collapse would not happen instantaneously – it would take centuries, probably millennia, to melt all of the Antarctica’s ice. But the destabilization of both Antarctic ice sheets could yield sea-level rises of a meter or so every 20 years – far outside the adaptation capacity for many countries and peoples (resulting in large-scale migrations and international conflict).
Australia – except perhaps the extreme north and Tasmania – will be unable to support significant crop production because of heat-waves and declining rainfall.
In India, with land temperatures soaring to 5 degrees or more above current levels, it will be too hot for most crops to survive. In western areas of the subcontinent, already arid areas get drier still, compounding the water emergency arising from the de-glaciation of the Himalaya and Karakoram mountain chains, forcing a human migration of hundreds of millions in search of food and water.
The world’s weather will grow increasingly haywire.
The 'angry summer' and civil war in Syria
Sariakandi Upazila, Bogra District
What are the consequences of global warming?
Two degrees may not sound like much, but it is enough to make most European summers as hot as 2003, when 30,000 people died from heatstroke. Extreme summers will be hotter still. Water shortages will be aggravated as the southern Mediterranean loses a fifth of its rainfall.
Two degrees is also enough to cause the collapse of the Greenland ice sheet, which would eventually raise global sea levels by seven meters (much of the ice-cap disappeared 125,000 years ago, when global temperatures were 1-2 C higher than now).
This melting will also continue to affect the world's mountain ranges. In Peru all the glaciers will disappear from the Andean peaks that currently supply Lima with water. In California, the loss of snowpack from the Sierra Nevada - three-quarters of which could disappear in the two-degree world - will leave cities such as Los Angeles increasingly thirsty during the summer. Global food supplies, especially in the tropics, will also be affected but while two degrees of warming will be survivable for most humans, a third of all species alive today may be driven to extinction as climate change wipes out their habitat.
Recent research offers more specific examples. On May 9, 2015, The Economist reported on work at Oxford University demonstrating the relationship between climate change and particular extreme weather events. One example given is the Australian heat wave of 2013 (‘the angry summer’), described as ‘virtually impossible’ without climate change. The article concludes:
'Worryingly, the risk of an extreme event seems to rise exponentially as mean temperatures creep up. The probability of a heat extreme is twice as great at 2°C of warming than at 1.5°C.'
Research from Columbia University illustrates how climate change acts as a ‘threat multiplier’, for example in relation to matters of national and international security. Drying and drought in Syria from 2006 to 2011—the worst on record — had a devastating impact on agriculture, causing many farming families to migrate to the cities. This influx, the researchers conclude, added to existing social stresses (including refugees from Iraq), which erupted into civil war.
The international security consequences of climate change have recently been considered in a report of the US Department of Defence:
'The National Security Strategy, issued in February 2015, is clear that climate change is an urgent and growing threat to our national security, contributing to increased natural disasters, refugee flows, and conflicts over basic resources such as food and water. These impacts are already occurring, and the scope, scale, and intensity of these impacts are projected to increase over time.'
Ocean acidification is sometimes referred to as ‘the other carbon dioxide problem’, or as ‘global warming’s evil twin’. The ocean currently absorbs about half of the CO2 emissions from burning fossil fuels, limiting the impact on global warming, but increasing ocean acidity. Seawater is depleted of the carbonate minerals that many sea creatures, from corals to plankton, use to build their shells or skeletons. This undermines the base of the ocean food chain, threatening the health and prosperity of all those who depend on the sea for sustenance and income.
IAP, the global network of science academies, issued a statement on ocean acidification in 2009, with the following headline messages:
Although different problems, global warming and ocean acidification have a common cause: anthropogenic CO2 emissions.
Already the pH of ocean surface water has decreased by 0.1, corresponding to a 26% increase in acidity. This is probably more acidic than at any point in the last 20 million years. The interaction of different stressors (such as global warming, ocean acidification and reduced levels of oxygen) makes it difficult to attribute specific observed consequences to ocean acidification. However, coral reefs, probably the world’s most important oceanic habitat, are already in decline almost everywhere, with as much as 27% having already been lost
Ocean acidification is projected to rise by 100-150% by 2100. Marine organisms will face progressively lower oxygen levels and high rates and magnitudes of ocean acidification, with associated risks exacerbated by rising ocean temperature extremes. Coral reefs and polar systems are particularly vulnerable.
LEGAL ACTION FOR THE CLIMATE GOAL: TOWARDS EQUITY, SURVIVAL AND THE RULE OF LAW
“PRESIDENT TRUMP MAY HAVE HIS ALTERNATIVE FACTS,
BUT ALTERNATIVE FACTS DO NOT WORK IN A COURTROOM”
Francisca Chagas dos Santos
‘Climate change will amplify existing risks and create new risks for natural and human systems. Risks are unevenly distributed and are generally greater for disadvantaged people and communities in countries at all levels of development.’[2.3]
‘Climate change is projected to undermine food security. Due to projected climate change by the mid-21st century and beyond, global marine species redistribution and marine biodiversity reduction in sensitive regions will challenge the sustained provision of fisheries productivity and other ecosystem services (high confidence).’[2.3.1, 2.3.2]
‘Climate change is projected to reduce renewable surface water and groundwater resources in most dry subtropical regions (robust evidence, high agreement), intensifying competition for water among sectors (limited evidence, medium agreement).’[2.3.1, 2.3.2]
‘Until mid-century, projected climate change will impact human health mainly by exacerbating health problems that already exist (very high confidence). Throughout the 21st century, climate change is expected to lead to increases in ill-health in many regions and especially in developing countries with low income, as compared to a baseline without climate change (high confidence).’[2.3.2]
‘In urban areas climate change is projected to increase risks for people, assets, economies and ecosystems, including risks from heat stress, storms and extreme precipitation, inland and coastal flooding, landslides, air pollution, drought, water scar- city, sea level rise and storm surges (very high confidence). These risks are amplified for those lacking essential infrastructure and services or living in exposed areas.’[2.3.2]
‘Aggregate economic losses accelerate with increasing temperature (limited evidence, high agreement).’[2.3.2]
‘Climate change is projected to increase displacement of people (medium evidence, high agreement). Populations that lack the resources for planned migration experience higher exposure to extreme weather events, particularly in developing countries with low income. Climate change can indirectly increase risks of violent conflicts by amplifying well-documented drivers of these conflicts such as poverty and economic shocks (medium confidence).’[2.3.2]
‘Without additional mitigation efforts beyond those in place today, and even with adaptation, warming by the end of the 21st century will lead to high to very high risk of severe, widespread and irreversible impacts globally (high confidence). In most scenarios without additional mitigation efforts ... warming is more likely than not to exceed 4 degrees C above pre-industrial levels by 2100.’[2.3]
It’s impossible to say with certainty: we have no experience of what awaits.A planet 4 degrees warmer would be hotter than at any time since the Miocene era some 25 million years ago (modern humans have been around for about 200,000 years).
Paleoclimatology and scientific modelling provide the basis for more detailed projections. Mark Lynas, a journalist and Research Associate at Oxford University’s Centre for the Environment, summarised the scientific research in his book, ‘Six Degrees: Our Future on a Hotter Planet’. The following projections derive from his work.
26 December 2016: Major flooding in UK now likely every year, warns lead climate adviser (The Guardian)
21 December 2016: California Forests Failing to Regrow After Intense Wildfires
13 February 2017: As Oceans Warm, Marine Life and People Who Depend on It, Struggle to Adapt(Inside Climate News)
14 August, 2016: 'The blob': how marine heatwaves are causing unprecedented climate chaos
"If we don't speak out now, if we don't raise our voice, then we will die."
Saul Luciano Lliuya
IPCC, AR5 projections
3 degrees Celsius may be the "tipping point" where global warming veers out of control, leaving us powerless to intervene as planetary temperatures soar. Computer model projections show worsening droughts making Amazonian trees, which have no evolved resistance to fire, much more susceptible to burning. Once this drying trend passes a critical threshold, any spark could light a firestorm. And once the trees have gone, desert will take its place. The carbon released by the forests' burning will be supplemented by more from the world's soils. This could boost global temperatures by a further 1.5ºC - tipping us straight into the four-degree world.
Three degrees alone would see increasing areas of the planet being rendered uninhabitable by drought and heat. In southern Africa, a huge expanse centered on Botswana could see a remobilization of old sand dunes, much as is projected to happen earlier in the US west. This would wipe out agriculture and drive tens of millions of climate refugees out of the area. The same situation could also occur in Australia, where most of the continent will fall outside the belts of regular rainfall.
In northern Europe and the UK, summer drought will alternate with extreme winter flooding as torrential rainstorms sweep in from the Atlantic - perhaps bringing storm surge flooding to vulnerable low-lying coastlines as sea levels continue to rise. Those areas still able to grow crops and feed themselves may find they are besieged by millions of climate refugees from the south.
With five degrees of global warming, an entirely new planet would come into being – one largely unrecognizable from the Earth we know today. The remaining ice sheets would eventually be eliminated from both poles. Rainforests have already burned up and disappeared. Rising sea levels have inundated coastal cities and are beginning to penetrate far inland into continental interiors. Humans will be herded into shrinking zones of habitability by the twin crises of drought and flood.
To find out what the planet would look like with five degrees of warming, one must largely abandon the models and venture far back into geological time, to the beginning of a period known as the Eocene. Fossils of sub-tropical species such as crocodiles and turtles have all been found in the Canadian high Arctic dating from the early Eocene, 55 million years ago, when the Earth experienced a sudden and dramatic global warming. These fossils even show that breadfruit trees were growing on the coast of Greenland, while the Arctic Ocean saw water temperatures of 20C within 200km of the North Pole itself. There was no ice at either pole; forests were probably growing in central Antarctica.
“If we don’t act boldly, the bill that could come due will be mass migrations, and cities submerged and nations displaced, and food supplies decimated, and conflicts born of despair.”
Barack Obama, September 2016