If mankind fails to curtail global warming, we will have to deal with fallout ranging from massive refugee crises and submerged cities to scorching heatwaves and drought, scientists say.
Here is what could happen if the negotiators and heads of state at COP21 come up empty handed:
Hotter temperatures: Without additional action, Earth could heat up by as much as four degrees Celsius by the end of the century, compared to pre-industrial levels. A mountain of scientific evidence tells us this would be a recipe for disaster. A "business as usual" emissions scenario would "lead to a very high risk of severe, widespread and irreversible" impacts, according to the UN Intergovernmental Panel on Climate Change (IPCC).
Rising seas: By 2100, the world's oceans would rise 26-82 centimetres (10-32 inches) over levels seen between 1986-2005, the IPCC found in its most recent assessment, which includes data up to 2012. More recent studies suggest the increases could be even higher. Driving the rise are ice sheets in Greenland and Antarctica shedding mass faster than ever, melting glaciers, and oceans that expand as they warm. Even a 2 C rise as targeted by the UN would submerge land currently occupied by 280 million people, according to Climate Central, a US-based research group.
The change could take a few hundred years, or up to 2,000 years. Extreme weather Superstorms, bone-chilling cold snaps and intense heat waves could become more common -- and more extreme -- due to global warming. While the link between specific weather events and climate remains hard to nail down, recent research has teased out climate change as an aggravating factor for deadly floods, snowstorms, typhoons and heat waves. Not all nasty hurricanes or heat waves, however, can be chalked up to climate change, scientists caution.
Water dilemma: Global warming can lead to long-running droughts and devastating floods, which means some parts of the world will not have enough water and others too much. Droughts in Syria and California have been tied to climate change. Heavy rains carry the risk of flooding that can send people fleeing for their lives, destroy homes and crops.
Humanitarian crises: Global warming can spur disease, ravage crops and push more people into poverty. Conflict over water or smaller harvests could instigate war or mass migration. People living on low-lying islands such as the Maldives, an archipelago in the Indian Ocean, or the Philippines could become climate refugees, forced to flee their homes due to rising seas. Impoverished people in the world are already being hurt by heat waves, drought and flooding, because they are both more dependent on the land and lack public services.
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The many health impacts of climate change
Medical experts say climate change affects human health in direct ways, by the spread of water- and mosquito-borne diseases for example, and indirectly, such as through hunger.
Here is a snapshot of the problem:
Thousands more dead: Between 2030 and 2050, climate change could result in nearly 250,000 deaths per year -- an estimated 38,000 from high temperatures, 48,000 deaths from diarrhoea, 60,000 from malaria and 95,000 from malnutrition, according to the World Health Organization (WHO). By 2030, the direct damage costs to health will be a whopping two to four billion US dollars per year, according to the WHO.
Cause and effect” It is not necessarily global warming itself that would lead to a cholera epidemic, but warmer temperatures conducive to deadly outbreaks. Scorching temperatures can cause cardiovascular and respiratory problems, especially in elderly people. During the widespread 2003 heatwave in Europe, more than 70,000 deaths were recorded. And with more sunlight comes more UV-related risks, like skin cancer. Climate change will also lead to increased deaths from natural disasters such as floods and hurricanes. Weather-related disasters have tripled since the 1960s, WHO says, adding that "every year, these disasters result in over 60,000 deaths, mainly in developing countries."
Infectious diseases: Global warming will facilitate the spread of infectious diseases which depend on carriers such as mosquitoes. WHO said that climate change is likely to lengthen the transmission seasons of these "vector-borne" diseases -- which are spread by a vector, or carrier -- and to alter their geographic range. Malaria already kills around 800,000 people per year, according to WHO. Mosquitoes also spread the deadly dengue fever, and some studies suggest that global warming could lead to two billion more people being at risk from the disease by 2080. The UN agency estimates that China will see an increase in a disease called Schistosomiasis, spread by snails in many underdeveloped regions. Some 240 million people worldwide already suffer from Schistosomiasis.
Pollution and asthma: An increase in forest fires caused by global warming, especially in the north, would result in more fine particles in the air. These particles are capable of penetrating deep into the lungs and can lead to lung cancer and asthma. Around 300 million people suffer from asthma worldwide, and WHO says the "ongoing temperature increases are expected to increase this burden." Warmer temperatures will also likely help allergy-inducing plants multiply, with Europe's pollen concentration expected to swell fourfold by 2050.
