What To Expect When The Planet Heats Up

Karina Collins
16 min readSep 5, 2021


Rising sea levels, floods, drought and food scarcity. In recent years, an increase in temperature of 1 degree Celsius, caused by global warming, has set Australia on fire, as well as Siberia, California, Argentina and elsewhere. Other global impacts include devastating storms and floods, mass destruction of corals, and sea level rise. Here, I explain the likely effects when temperatures rise by 3, 4 and 5 degrees Celsius.

Forest fire near Athens, Greece. Photo: © rudy_ath CC-by-Sa-3.0

Rising Temperatures: 3 Possible Scenarios

In this article we look at three basic scenarios for what we can expect in the way of rising temperatures, and what the impact on the planetary biosphere is likely to be. These scenarios represent “likely” (3°C), “possible” (4°C) and (hopefully) “worst-case” (5°C) outcomes. The last-mentioned is the most pessimistic “representative concentration pathway” entitled “RCP 8.5”, which was outlined in the IPCC’s Fifth Assessment Report (2014).

One word of warning: all global temperature projections are data-driven guesstimates, based on complex mathematical assumptions that may or may not materialize. The truth is, no one knows for sure how global warming will develop, whether it is still reversible, or what effects it will have on our environment.

We do know, however, that extreme weather events, such as droughts and heatwaves, are becoming more frequent and more severe because of climate change.

This does not mean that the climate change denial machine is right when it says climate change doesn’t exist. It simply means we don’t know how bad things are going to get, or how quickly.

In This Article:

  • Rising Temperatures: 3 Possible Scenarios
  • Scientists Warn About Rising Temperatures. Politicians Dither.
  • What Are The 4 Big Unknowns Of Global Warming?
  • How High Could Temperatures Go?
  • What Effect Will an Extra 3.5 Billion People Have on Energy Consumption?
  • When Can We Expect to Reach an Irreversible Tipping Point?
  • How High Will Sea Levels Rise?
  • What Are The Effects Of Rising Temperatures?
  • Plus Three Degrees Celsius
  • Plus Four Degrees Celsius
  • Plus Five Degrees Celsius
  • Conclusion: Rising Temperatures Are Very Bad News
  • References

Scientists Warn About Rising Temperatures. Politicians Dither.

Ever since 1992, the United Nations has been trying to agree solutions to the growing problem of climate change, which now threatens to engulf the planet. Its latest attempt at diplomacy was the Paris Climate Agreement (2015), hammered together by delegates from 196 countries, who pledged to keep global warming below 2°C (3.6°F) while trying to limit temperature increase to 1.5°C (2.7°F).

This was followed by strong-worded advice from the Intergovernmental Panel on Climate Change — the U.N.’s lead agency on climate science — in their Special Report on Global Warming of 1.5°C, published in October 2018.

The report gave a blunt assessment of the effects of global warming, and explained in detail how much worse they would be at 2 degrees of warming than at 1.5 degrees.

The report specified two mid-term goals which the global community should aim to achieve if it wanted to limit Earth’s temperature to 1.5°C by the end of the century. First, by about 2030, greenhouse gas emissions needed to be reduced by about 45 percent from 2010 levels. Second, by about 2050, emissions needed to fall to net-zero.

To achieve warming of no more than 2°C, the required reductions were 20 percent by 2030, and net-zero by 2075. (1)

The IPCC emphasized the necessity for deep cuts in the consumption of fossil fuels — the main source of greenhouse gases — and warned about the need for rapid, far-reaching and unprecedented changes in all aspects of society.”

Since Paris, despite the IPCC’s special report and numerous other studies, there has been much talk, quite a lot of action on renewable sources of energy, but no actual progress on cutting emissions. As of Sept 2019, greenhouse gas emissions are still rising, energy consumption is rising, and fossil fuel consumption is as high as ever.

As a result, the greenhouse effect is getting stronger, the environmental effects of fossil fuels are getting worse, and all the time temperatures are rising. Meantime, some experts are saying: Our Climate Plan Can’t Cope.

What Are The 4 Big Unknowns Of Global Warming?

There are three big questions when it comes to predicting the effects of rising temperatures on Earth’s climate system — three questions, but no reliable answers.

An Australian bushfire burns out of control, January 2020. According to NASA calculations, as of January 2, 2020, the 2019–20 bushfire season accounted for 306 million tonnes of carbon dioxide being released into the atmosphere. The fires also release vast amounts of lung-choking particulate matter and other aerosols of partially combusted black carbon and soot. Photo: 80 trading 24/CC BY-SA 3.0

How High Could Temperatures Go?

Nobody knows. No one knows how hot it’s going to get, or what the consequences will be. All we know is that the effects of global warming on humans are nothing compared to the likely effects on the biodiversity of other living creatures and their habitats.

What Effect Will an Extra 3.5 Billion People Have on Energy Consumption?

Scientists are already predicting a 50–90 percent increase in food demand by 2050, so it looks like the demand for energy could skyrocket. If so, kiss goodbye to 1.5, 2.0 and even 3.0 degrees of warming.

When Can We Expect to Reach an Irreversible Tipping Point?

The largest repositories of carbon in the global carbon cycle, include: the ocean, the polar ice caps, mountain glaciers, the soil, and the world’s forests. All are under severe climate pressure to release carbon dioxide into the atmosphere, but the big question is — at what point is this likely to happen? When will one of these huge carbon reservoirs finally succumb — when the temperature reaches 2.5 degrees? Or 3.7 degrees? Or 4.4 degrees? Because if it does happen, all bets about global temperatures are off.

A key example is the tipping point at which the unique wet biome of the Amazon Rainforest starts mutating into a drier ecosystem, via a process known as savannization. (2) Such a transformation would have incalculable consequences for the world’s climate.

The tipping point was traditionally thought to occur when deforestation of the Amazon reaches 40 percent (it currently stands at 17 percent), but a combination of climate-induced drought as well as natural and man-made fires leads scientists to believe that it might be reached much earlier — after only 20–25 percent deforestation.(3)

In truth, we’re talking about not one but a series of climate tipping points, which will lead the Amazon into an irreversible sequence of changes. This may account for the differences between scientists as to the onset of the savannization process.

How High Will Sea Levels Rise?

Sea level rise (SLR) is the go-to climate nightmare — the one scenario that no one can ignore, because it would be a transformational experience for the world as a whole. A rise of six feet, for instance, anticipated by at least one specialist study, would swamp cities like Shanghai and Mumbai (to name but two), and displace around 12 million people in U.S. coastal cities.

Miami, for example, home to about 2.5 million people who live less than 6 feet above sea level, would be flooded if not submerged. (4) At present, scientists who predict this level of SLR are characterized as incorrigible jeremiahs, but perhaps not for much longer.

South Beach, Miami. What it could look like if temperatures rise by 2 degrees Celsius. Photo: © Nickolay Lamm/ClimateCentral. (5)

What Are The Effects Of Rising Temperatures?

Here is a short summary of the possible global consequences of rising temperatures. (Note: all temperature increases are related to the pre-industrial baseline, 1850–1900.) Much of it is informed guesswork rather than inferences from climate models, but it may still offer important insights into what lies ahead.

Plus Three Degrees Celsius

Assuming the world does not drastically reduce its emissions, but assuming that all Paris pledges (Nationally Determined Contributions) are implemented up to 2100, the IPCC believes that warming will reach 3 degrees Celsius (above the 19th century baseline) by the end of the century. (1)

Effects of a 3 °C rise in temperature

• At three degrees of warming, heatwaves increase in number, intensity and duration. The years 2014–2019 (when warming was only one degree), produced a series of record-breaking heat spells around the globe, killing thousands. At 3°C the situation will be very significantly worse.

• Food scarcity starts becoming a very serious problem for hundreds of millions of people mostly in developing countries. Grain yields decline by 10 percent for every degree Celsius above 30°C, and at 40°C they are zero. 6

• Some scientists think that a three-degree increase in global temperature will throw the carbon cycle into reverse, so instead of absorbing CO2, vegetation and soils will begin releasing it. Soil contains roughly 1,500 billion tons of CO2, and as soil warms, micro-bacteria will accelerate the breakdown of this carbon into the atmosphere.

• Australia could become a death trap. With rising temperatures, along with more intense heatwaves and regular droughts, cattle grazing will become unviable and food production is likely to seriously decline. Salt water will creep up the dwindling rivers, poisoning ground water. In the cities heat is likely to kill 10,000 elderly people each year.

• Africa will fare no better. The moderate drought of 2001 forced hundreds of thousands to rely on food aid, but aid will be scarcer as world supplies are stretched to breaking point.

• The Indian subcontinent will be choking on dust. With rising temperatures and no effective reductions in coal plant emissions or fuelwood burning, cities will become toxic from air pollution and smog, especially during the dry season. At one degree of warming, Delhi is already the most polluted urban area on earth, suffering 10,000 pollution-related deaths every year. (7) Imagine how Delhi and other Indian cities will be at 3 degrees.

• In general, starving people will be on the move around the world. In Europe and the United States fascist-style leaders will win votes by blocking and demonising these new climate refugees.

• Global water supplies will come under threat, as mountain glaciers disappear. In the past, these would have provided valuable supplies of freshwater during dry periods.

• In addition, warmer air holds more water. This causes longer periods of drought and big deluges when rainfall finally arrives. Then, because of withered trees, grasses and other vegetation, the falling rain is not absorbed by the soil and simply runs off, causing floods in the process. Green infrastructure projects such as ‘sponge cities‘ will be invaluable in the fight against the twin threats of flooding and heatwaves.

• Mosquitos, and other types of virus-carrying insects breed faster in warm, humid weather. Shifting weather patterns also broaden their habitat. Even at one degree of warming, malaria is being carried into upland areas of East Africa that were previously malaria-free. So, at three degrees there is sure to be a significant increase in the incidence of infectious diseases.

• Ozone-related smog gets denser as the temperature rises, so all large urban areas that are susceptible to this type of air pollution are likely to experience greater levels of toxic haze.

• Wildfires, which occur more often with drought and high temperatures, will add significantly to air pollution. In the summer of 2019, Arctic fires in the Siberian taiga created smoke clouds that covered more than 5 million square kilometers — larger than the area of the European Union. 8 Not long afterwards, parts of South America were covered in smoke from Australian bushfires that blazed across NSW and Victoria.

• Back in the early 2000s, with less than one degree of warming, air pollution caused an estimated 200,000 premature deaths annually in the United States alone. (9) Globally, according to the World Health Organization (WHO) the figure was 7 million fatalities. Imagine the casualties when warming rises to 3°C.

• The higher the temperature, the longer the pollen season. Bad news for the 25 million Americans with asthma, and the 1 in 13 around the world who also suffer from it. (10) At one degree of warming, Asthma already kills around 1,000 people every day. (11)

• Climatologists at the non-profit organisation Climate Central calculate that 275 million people (80 percent of whom are in Asia) live in areas that will be flooded if global warming reaches 3°C. Although sea levels won’t rise immediately that the 3°C threshold is reached, the rises will be “locked in” at a temperature rise of 3°C, meaning they will happen even if warming slows down. (12)

• The Amazon Rainforest could experience runaway savannization. New climate models suggest that by the year 2050, temperatures in the Amazon will rise by 2–3°C. This coupled with a decrease in precipitation during dry months might trigger widespread and irreversible drying. Research conducted by Brazil’s National Space Research Institute (INPE) — indicates that a warmer, drier climate could convert between 30 percent and 60 percent of the Amazon biome into a type of dry savanna. (13) (14)

• Loss of habitat will be a huge problem for many species of animals (e.g. polar bears, emperor penguins), insects and plants. Roughly 49 percent of insects, 44 percent of plants and 26 percent of vertebrates are likely to lose more than half of their habitats. (15)It’s worth remembering that humans rely on plants, insects and other animals to provide crop pollination, pest control, water quality, soil conservation and flood prevention.

Plus Four Degrees Celsius

According to its recent 500-page environmental impact statement on the deregulation of car exhaust emissions, the U.S. National Highway Traffic Safety Administration believes global warming will reach 4 degrees Celsius. (16)

Effects of a 4 °C rise in temperature

In addition to the consequences, listed above, a four-degree increase in Earth’s temperature will attract additional consequences, as follows. (17 (18)

• A significant fraction of the ice sheets in Greenland and Antarctica will melt, causing a rise in sea level of about three meters (10 feet).

• Low-lying tropical islands and most Pacific atoll countries are likely to be uninhabitable.

• Elsewhere, Osaka, Japan (population affected: 5.2 million), Alexandria and surroundings, Egypt (population affected: 8 million), Rio de Janeiro, Brazil (population affected: 1.8 million), and Shanghai, China (population affected: 17.5 million) will be submerged. There are many other highly vulnerable cities in Mexico, Venezuela, Mozambique, Madagascar, India, Bangladesh, Indonesia, the Philippines, and Vietnam.

• Almost the entire population of New Orleans, will find themselves underwater. Almost 5.6 million people and a third of all of the homes in Florida will be submerged. Flooding will only affect around 9 percent of New York City, but that’s 700,000 people. Houston, Atlantic City, Charleston, and Boston will be severely impacted. These are impacts of 10 feet of calm water in windless conditions. Factor in a storm and you can add at least an extra 4–5 feet of flooding.

• In general, sea-level rise is likely to be 15 to 20 percent higher in the tropics than the global average, as coastlines are deprived of their protection, usually provided by coral reefs and mangroves (both now destroyed), against contamination and erosion.

• Oxford, England, would sit on one of many coastlines in a Britain transformed into an archipelago of tiny islands. Elsewhere, the Thames Valley, and towns around the already vulnerable Severn estuary like Bristol, will be among the regions worst affected. In addition, almost the whole of the English coast from the Isle of Wight to Middlesbrough will be at a very high risk of inundation.

• The abandonment of coastal cities because of floods, or whole regions like the Mediterranean Basin (or even whole countries in Saharan Africa) due to unbearable heat, will create a mass of climate refugees that are likely to overwhelm the Baltic countries, Scandinavia and European Russia. The rest of the world will experience similar migrations.

• One of the world’s biggest carbon reservoirs — the northern permafrost — will succumb to irreversible thawing. The latest estimates suggest that the top 3 meters (10 feet) of the permafrost contains a staggering 1,000 billion tons of organic carbon. (19) How much will all this add to global warming? Nobody knows, but the mathematics is scary.

• The impacts of the rising temperatures and extreme heatwaves that are predicted to occur in a 4°C world will greatly exceed the adverse effects experienced to date (heat-related fatalities, wildfires, crop losses) and may exceed the adaptive capacities of many societies and systems, especially in tropical and sub-tropical zones. Average monthly summer temperatures would increase by 6–9°C in large areas of the world, including North Africa, the Mediterranean and the Middle East.

• Temperatures in southern England will reach 45°C — the sort of heat found in Marrakech, today. Air-conditioning will be essential for anyone who wants to stay cool, placing extra stress on energy consumption and power systems.

• Large-scale loss of biodiversity through extinction of species is likely to occur. Ecosystems will be impacted by greater deforestation due to droughts and wildfire, aggravated by changes in land use and agricultural expansion. Marine life will be most severely affected as coral reefs collapse, leading to a major loss of habitat for a major proportion of marine organisms.

• China’s agricultural production will implode as it attempts to feed 1.5 billion people on less than two-thirds of current food levels. Indeed, for people throughout the world, food scarcity if not starvation will be an ever-present reality. For example, significant decreases in crop yields have been observed in the United States for corn at temperatures of 29°C, and soybeans at 30°C. On top of this is the impact of saline contamination (from seawater) on agricultural land in fertile delta areas, in countries like Bangladesh, Egypt, Vietnam, and parts of the west African coast.

• Freshwater supplies, already seriously reduced in a 3°C world, will be severely stretched. Runoff (the rapid drainage of water from the land surface into rivers and streams) will increase significantly, depleting supplies and stocks of freshwater. Monsoon river deltas, like the Ganges and Nile, are especially vulnerable to changes in the seasonality of runoff, which will impact adversely on water availability. Annual runoff here is forecast to increase by roughly 40 percent in both river basins.

• Against a backdrop of steadily rising temperatures, infectious illnesses and vector-borne diseases (like malaria and dengue fever) will continue to invade and take over areas where it was too cold for them to thrive in the past.

• It goes without saying that scarcity of food and freshwater, allied to searing heat and increasing risk of illness, is bound to cause enormous suffering for hundreds of millions, possibly billions, of people around the world. The number of possible fatalities runs into the millions, as disease and malnutrition take their toll.

Plus Five Degrees Celsius

If the world takes no effective climate action, the IPCC predict a rise to between 4.8 and 5.7 degrees Celsius. This is the worst-case “representative concentration pathway” entitled “RCP 8.5”, which was outlined in the IPCC’s Fifth Assessment Report (2014).

Effects of a 5 °C rise in temperature

In addition to the consequences, listed above, for those affected by three and four degrees of warming, a five-degree world will attract even more severe consequences, as follows.

• In this scenario, the planet is quite different. All Arctic sea ice has disappeared and the Antarctic ice sheet is dwindling. Rainforests have turned into savanna or desert. The Alps are completely dry and now resemble the High Atlas Mountains in Morocco. With many tropical zones now scorched and dried out, the Canadian and Siberian lands of the far north now represent the most appealing real estate on the planet.

• Sea levels are continuing to rise, pushing deep into continental interiors, redrawing the map in the process. In America, the state of Florida is now ocean, while the Gulf Coast and the entire Atlantic seaboard is submerged. In Europe, London and the east coast of England up to Middlesbrough is underwater. The Netherlands has also disappeared, so too has Denmark as well as Riga, Tallinn, Stockholm, Helsinki, most of the Baltic coastline and the lowlands of northern Germany. Venice, Trieste and Verona are also submerged.

In China, rising temperatures have caused Shanghai to become submerged and there is now nothing but sea between Beijing, Wuhan and where Shanghai used to be. Hong Kong has disappeared too, as have Phnom Penh, Ho Chi Minh City, Singapore, Bangkok, Dhaka, Mumbai, and Baghdad.

• Life is a continuous quest for food and security with continuous waves of climate refugees invading the continental uplands in search of shelter, upsetting indigenous populations who see them as intruders.

• The global community with its stock markets, commodity exchanges, 5G networks, Internet, Cloud computing, mobile phones, laptops, online trading systems and paper currencies has collapsed, leaving power and influence in the hands of competing enclaves powered by whatever fossil fuels are available, and run by military-style authorities.

• For a glimpse into this future world of 5°C warming, take a look at present-day collapsed states like Somalia, where conflicts over scarce food and other resources have led to violence and anarchy, and a male life expectancy of 53 years. (20)

Conclusion: Rising Temperatures Are Very Bad News

Unrestrained fossil fuel consumption — with its private jets, 5-star hotels, fast cars, seafront properties, luxury shopping malls and global brands — does not create a healthy, safe or worthwhile type of existence. Instead, it leads to a real climate crisis with rapidly rising temperatures, the savannization of the tropical rainforest, runaway polar ice-melt and permafrost-thaw, a huge rise in sea levels and the extinction of species and habitats beyond our comprehension.

Finally, see: What is climate change denial?


  1. IPCC Special Report on Global Warming of 1.5°C. (2018) Summary for policy makers.
  2. Testing the Amazon savannization hypothesis: fire effects on invasion of a neotropical forest by native cerrado and exotic pasture grasses.” Divino V. Silvério, Paulo M. Brando, Jennifer K. Balch, Francis E. Putz, Daniel C. Nepstad, Claudinei Oliveira-Santos, Mercedes M. C. Bustamante. The Royal Society. June 5, 2013.
  3. Land-use and climate change risks in the Amazon and the need of a novel sustainable development paradigm.” Carlos A. Nobre, Gilvan Sampaio, Laura S. Borma, Juan Carlos Castilla-Rubio, Jose S. Silva, Manoel Cardoso. PNAS September 27, 2016 113 (39) 10759–10768.
  4. Contribution of Antarctica to past and future sea-level rise.” Robert M. DeConto & David Pollard. Nature. Vol 531, p.591. March 2016.
  5. Visualizing Sea Level Rise” ClimateCentral
  6. “Rising Temperatures and Rising Seas: The Crop Yield Effect.” Lester R. Brown. Earth Policy Institute.
  7. “Delhi’s Air Has Become a Lethal Hazard and Nobody Seems to Know What to Do About It”. Time magazine. 10 February 2014.
  8. World Meteorological Organization. August 2019.
  9. Air pollution and early deaths in the United States. Part I: Quantifying the impact of major sectors in 2005.” Fabio Caiazzo Akshay Ashok, Ian A. Waitz, Steve H.L. Yim, Steven R.H.Barrett. Atmospheric Environment. Volume 79, November 2013, pp 198–208.
  10. CDC.gov. 2019
  11. Global Asthma Report 2018.
  12. “The three-degree world: the cities that will be drowned by global warming.” Josh Holder, Niko Kommenda, Jonathan Watts. The Guardian. Fri 3 Nov 2017.
  13. Climate change in the Amazon.”
  14. Will Deforestation and Warming Push the Amazon to a Tipping Point?” Carlos Nobre. Sept 4, 2019.
  15. “Insects face calamitous habitat loss.” Tim Radford. Climate News Network. May 21st, 2018.
  16. “Trump administration sees a 7-degree rise in global temperatures by 2100.” Juliet Eilperin, Brady Dennis, Chris Mooney. Washington Post. September 28, 2018.
  17. “Turn down the heat — Why a 4°C warmer world must be avoided.” Potsdam Institute for Climate Change, Climate Analytics. 2012.
  18. Rising Temperatures — A degree by degree explanation of what will happen when the earth warms“. Retrieved Oct 9, 2019.
  19. “Soil organic carbon pools in the northern circumpolar permafrost region.” (PDF). Tarnocai, C., Canadell, J.G., Schuur, E.A.G., Kuhry, P., Mazhitova, G., Zimov, S. (2009). Global Biogeochemical Cycles. 23 (2): GB2023.
  20. Somalia: World Health Organization. (PDF)



Karina Collins

I work in marketing by day — and pen my thoughts on climate change by night.