Because of the ‘urban heat island effect’ cities are already warmer than their rural surroundings. If we do not curb emissions (Business-As-Usual scenario – RCP 8.5) by 2100 they will be much hotter still. Climate Central in 2017 created the interactive map below in partnership with the World Meteorological Organization.
Under the BAU-scenario cities in the Balkans will experience the most extreme temperature rise, varying between 7.5°C and 8.5°C increase. For example Budapest will reach an average summer daily maximum temperature of 32.2 °C (from 24.8°C ), Sofia 32.6°C (from 24.3°C) and Bucharest 36.4°C (from 28.1°C ). Temperature-wise this would transform the Balkans into the Middle East.
At their turn some cities in the Middle East will get so hot that they have no current-day equivalents. For example, Riyadh will reach 48 °C Celsius and Baghdad a blistering 49,5 °C .
The temperatures in the graph refer to average daily maximum temperatures over June, July and August on the Northern Hemisphere (Dec, Jan & Feb on the Southern Hemisphere).
Researchers at MIT warn that if climate change remains unchecked (Business As Usual-scenario = RCP 8.5) over half a billion people will, from 2070 onwards, experience humid heat waves that will kill even healthy people in the shade within 6 hours. The Wet Bulb Temperature (WBT) would exceed 35°C (95°F), at which the body – of any mammal – cannot cool itself, overheats and shuts down.
Three regions were studied: China (2018), South Asia (2017) and the Persian Gulf (2015). The researchers predict (at RCP 8.5) WBT exceeding 35°C about once every decade for the Northern Plains in China (400+ million people), at locations in the Chota Nagpur plateau, northeastern India, and Bangladesh in South Asia (70+ million people). Persian Gulf regions that would be affected include cities such as Doha, Qatar, Abu Dhabi, Dubai (UAE) and Bandar Abbas (Iran).
The total number of people affected will be higher than 0.5 billion. A study in Nature (2017) identifies regions worldwide that are likely to exceed the survivability threshold from 2070 onwards (see Fig. 2). These also include the Eastern United States, Northern Latin America and Northern Australia.
Wet bulb temperatures higher than 33.5°C for more than a few hours have not been measured in human history (yet). In 2015 there was a severe episode in South Asia with 30°C WBT. This led to 3,500 deaths. According to this article the largest hospital in Karachi was receiving 1 patient per minute and the morgue was overflowing.
Would airconditioning be to avail? Podcast Ashesashes describes that a ‘perfect storm’ will hit power supply at extreme temperatures. Airconditioning at high temperatures leads to more than 20% extra power demand, while at the same the power grid becomes less effective, nuclear and gas fuel plants provide less power because of warmer cooling water and transformers are more likely to overheat leading to power outages. Also, it is hard to see how renewable energy could meet the peak demand. Without solutions, the areas mentioned would effectively become uninhabitable.
At the Business as Usual-scenario many billions of people would experience WBT higher than 32°C on a regular (e.g. yearly) basis, which is already deadly for the less fit and makes working outside impossible.
A study in Nature Communications (2019) finds that if greenhouse emissions continue unabated (RCP 8.5) climates in North America will shift on average 850 kilometers between now and 2080. That is, 14 kilometers per year. The northeast will tend to feel more like humid subtropical parts of the Midwest or southeastern U.S – warmer and wetter. Washington will be like northern Mississippi. San Francisco will be like L.A. And New York will be like northern Arkansas.
Another study from 2019 describes that in 2070 Minnesota’s signature forests might be lost altogether to prairies. Researchers describe that if we are to hit 667ppm CO2-equivalent greenhouse gases in 2070 Minnesota by then might resemble Kansas. They describe that the state’s tree cover would creep northward and the prairies that predominate in the southwest of the state would take over what was previously a mix of fields, deciduous woods and pine forests. Also, the say that climate is likely to change too fast for plant species to migrate to their new locations. Plant species would need help by moving them (sic!).
When we turn to Europe, it is harder to find climate analogue studies. A Swedish government study from 2007 predicts (conservatively we might add in 2018) an average temperature rise by 2080 in between 3 and 5°C. Climate modelling based on these numbers would mean that the area around Stockholm would have a climate comparable to Northern France.
The warm gulf stream is a current that brings warm water from the tropics to the poles, where it cools, sinks and returns southwards. It weakens because 1) warming makes water less dense and more buoyant and 2) fresh and cold water from the melting Greenland ice sheet disrupts the flow.
The warm gulf stream has weakened about 15% since 1950. Past collapses of the gulf stream have caused western Europe to descend into freezing winters. A significantly weakened system is associated with more – maybe much more – severe storms in Europe, faster sea level rise on the east coast of the US, increasing drought in the Sahel and collapsing deap sea ecosystems.
is said to be highly non-linear and has been associated with abrupt changes in
temperature when disturbed, such as winter temperatures changing up to 10C
within three years in some places.
Counterintuitively, the cooler water close to western Europe that is entailed in a weaker gulf stream helps warm air to flood into Europe from the south, thereby also possibly increasing summer heatwaves.
Under the Business-as-usual scenario (RCP 8.5) the future climates in 2030 will most closely resemble Mid-Pliocene climates, with surface temperatures 1.8 °C to 3.6 °C warmer than preindustrial temperatures. This means a climate that resembles the climate 3-3.3 million years ago, when CO2 -levels were at 400ppm – levels which we have crossed in 2016. Mid-Pliocene conditions will first emerge in continental interiors and in the decades afterward they will spread towards the coasts.
In 2100 the situation will be totally different. Under the RCP8.5 scenario, the climate from the past that best matches continental interiors by 2100 is the early Eocene climate. For these climate conditions, we have to go back abut 50 million years, when global mean annual surface temperatures were a whopping 13 °C ± 2.6 °C higher than preindustrial temperatures and there were swampy forests in the arctic.
Under the RCP4.5 emission scenario the climate stabilizes at mid Pliocene-like conditions.
Researchers at the University of South Wales, using data from 43,000 rainfall stations and 5,300 river monitoring sites across 160 countries, have found (2018) that water supplies worldwide are decreasing. Despite growing precipitation due to climate change, higher evaporation rates and dryer grounds that soak up more water leads to less water in rivers.
This study is in line with a study from 2009, that points out that world’s major rivers, amongst which the Yellow river in Northern China and the Ganges in India, are ‘drying up’. Causes are human activities such as dam building and diverting water for agriculture (that caused e.g. the Aral Sea to disappear) and climate change altering rainfall patterns and increasing evaporation rates. The only exceptions are rivers in the Arctic, the Brahmaputra in South Asia and the Yangtze in China. Very much likely because of additional melting of glaciers and ice sheets.
Experts predict that water levels of Euphrate and Tigris might drop 30-70% compared to end 20th century and speak about the “Fertile Crescent” disappearing altogether. Even notoriously wet places such as the United Kingdom are expecting severe water shortages by 2050s as summers get drier. The Colorado river has no longer enough water to go around.
Most of northern china suffers from acute water shortage (multicausal). In the past 25 years, 28,000 rivers and waterways have disappeared across the country. The iconic Yellow River, the second-longest in Asia, is now a tenth of what it was in the 1940s, and often fails to reach the sea. Former Chinese premier Wen Jiabao has warned the lack of water threatened the very survival of the Chinese nation itself.
A United Nations report of 2009 estimated the number of people to be displaced internally in 2045 by desertification alone around 135 million.
The UN International Organization for Migration forecasts 200 million internal and international (permanent and temporary) environmental migrants by 2050.
A paper from June 2017 (by Geisler et al) mentions 1.4 billion people that could be climate refugees by 2060 due to rising ocean levels (alone!). A number that societies might not be able to support: “The colliding forces of human fertility, submerging coastal zones, residential retreat, and impediments to inland resettlement is a huge problem. We offer preliminary estimates of the lands unlikely to support new waves of climate refugees due to the residues of war, exhausted natural resources, declining net primary productivity, desertification [and] urban sprawl…”
12 million hectares of productive land become barren every year due to desertification and drought (alone), while food production needs to increase by 70% in 2050 to feed the entire world population. Drought, water scarcity and destruction of natural resources because of climate change (and overpopulation, etc.) might lead to conflict. The UNCCD reminds that 40 per cent of all intrastate conflicts in the past 60 years are linked to the control and allocation of natural resources.
In addition to a weakening gulf stream,another factor that contributes to colder winters (and probably warmer summers) in the northeastern United States, Europe, and especially Asia, is a weakening jet stream. The jet stream is a wind of about 180 km/h on average and up to 400 km/h in instances, that streaks around the north pole at 8km altitude. It gets its power from temperature differences between south and north. It is weakening because the arctic is warming fast. Warming in the arctic means less sea ice, which means more – dark – ocean that in turn absorbs more heat (i.e. a positive feedback loop).
A weaker jet stream meanders more, bringing warmer air to pockets in the arctic and colder air to pockets south. These ‘loops’ in the jet stream can get stuck, bringing about extreme events of cold spells and probably also heat and drought. Based on changes in the jet stream researcher predicted worsening drought in California back in 2004. The weaker jet stream does not mean that cold spells get colder though, cold extremes are getting less cold.
3-3.3 million years ago global average temperature was 2-3 °C higher than today. The sea level was 25 meters higher and there was hardly any ice sheet in the northern hemisphere. Just as in predictive models, in the paleaontological data you also see a larger difference with today’s temperatures in the northern hemisphere than in tropical regions and southern hemisphere.
Carbon dioxide concentration during the mid-Pliocene has been estimated at around 400 ppm (yes, the 400 ppm that we have crossed in 2016 for the first time in 3 million years).
The climate was not only warmer, but also wetter, resulting in a northward shift of the taiga (boreal forest) and tundra and a spread of tropical savannahs and woodland in Africa at the expense of deserts (am I reading this correctly: less desert?!)
The Guardian dedicates an article to where you can best live in the U.S. when climate change gets serious. Broadly speaking you can best move to a band roughly above the 42nd parallel.
Places close to a reliable source of water without being flood-prone score high. Seattle, Buffalo, New York (with flood defenses), and Duluth, Minnesota are mentioned as places you might want to be at the end of the 21st century. Places that score low are the south-west and south-east because they will be baked. Southern Florida will be submerged and the Gulf coast will be battered by hurricanes.