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Consider an area of a fantasy world which experiences the following changes:

  • Amount on rainfall, and thunderstorms, increases dramatically.
  • Average temperature increases by 10-20 degrees Celsius over a period of two years (depending on how cold the location originally was; there is some variance in the temperature of the region).

What happens to forests, fields and livestock? Will the place be a decaying apocalyptic wasteland (with forests and fields rotting where they used to grow, and livestock and game animals dying of exhaustion), or will there be enough crops and remains of an ecosystem for people to survive without a significant loss of population?

In the long run species more adapted to the new climate will certainly take over, but I am more interested in what happens within the transitory period; up to five years, for example.

A climate change of 2 degrees is considered to significantly change agriculture; a change one order of magnitude will do more. On the other hand, many animals can survive such a change (some people take a vacation in the sunny south during the coldest winter, for example), if they have something to eat. I do not know about plants.

Details

Before the changes above, the area is a more-or-less stereotypical fantasy setting - flora, fauna and climate are roughly similar to central to northern medieval Europe, as is culture. There is lots of uninhabited woodland and hills. The population is fairly small and scattered; this is a backwater of a larger civilization.

The area is limited by mountain ranges, a desert, and a large swampland, where the temperature gradually changes from the previously abnormally cold to that of the surrounding areas.

Context

I'm running a fantasy roleplaying game, and due to a powerful nature spirit leaving and another filling the power vacuum, the mentioned environmental effects happen. These forces do not otherwise actively change the life of living things in the area. There is other magic, but I am not interested in what effects it might or might not have. I want to know what will happen if none of there powerful unrealistic forces take notice and act.

(In the context of roleplaying, this will give the player character room to do something about the events, or to ignore them, as they will, and with consequences.)

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  • $\begingroup$ Hello Tommi Brander, and welcome to Worldbuilding! This looks like a fantastic question, especially for a first post on the site. Please visit our help center and take the tour to learn more about the site. $\endgroup$ – Gryphon - Reinstate Monica May 14 '18 at 17:55
  • $\begingroup$ Can we be a little more specific about "10-20 degrees Celsius" part? For example, today London has year average temperature of 10.3 C. Adding 10C would make it hotter than Barcelona - something like New Orleans. Adding 20C would push yearly average above 30C, which is not common anywhere on Earth today. $\endgroup$ – Alexander May 14 '18 at 18:16
  • $\begingroup$ @AlexP I tried to clarify. I am interested in the process - will the plants just die when it gets hot, or will they struggle but survive until the adapted species arrive. What about livestock? $\endgroup$ – Tommi Brander May 14 '18 at 18:16
  • $\begingroup$ @Alexander +20 for colder parts of the area, +10 for the hotter parts. $\endgroup$ – Tommi Brander May 14 '18 at 18:20
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    $\begingroup$ It depends on what the final temperature is. Photosynthesis is temperature dependent, reaching a max between 35-45°C (depending on whether it's C3 or C4 photosynthesis), and shutting down entirely over about 55°C. Also, many temperate-zone plants require some time at low temperatures ("chilling hours") to set fruit: en.wikipedia.org/wiki/Chilling_requirement $\endgroup$ – jamesqf May 14 '18 at 18:20
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There is a lot of difference between 10° C and 20° C.

Let's take as a starting point Stockholm in Sweden: average temperature 7.6° C, average low 4.5° C (from −3.9° C in February to 14.5° C in July), average high 10.7° C (from 0.5° C in January to 23° C in July); it rains all year round, with a total of 531 mm/year. (One wouldn't think of it as such, but Stockholm receives less total precipitation than Rome and even Bucharest.)

10° C warmer

Consider Naples in Italy: average temperature 15.9° C (8.3° C warmer), average low 11.0° C (from 4.4° C in January to 19.1° C in August), average high 20.8° C (from 13° C in January to a whopping 30.3° C in August); it rains from September to April, with a total of about 1,000 mm/year (twice as much as in Stockholm, but the summers are drier). While the spontaneous flora is quite different it is not entirely different, and Italians can grow all the plants Swedes can grow, plus some which won't grow in Sweden.

Overall, a 10° C warming going from the climate of Scandinavia to the climate of Italy would be survivable, and, as a bonus, people will have the opportunity to grow grapes and olives and oranges.

20° C warmer

Consider Jakarta in Indonesia: average temperature 26.7° C (19° C higher), average low 23.3° C (year round), average high 30.1° C (year round); it rains all year round, with a total of 1,816 mm/year (3 times the amount of rain which falls in Stockholm). There is very little in common between the spontaneous or cultivated plants of Scandinavia and Indonesia. Some of the plants which grow in Sweden can also be grown in Indonesia, but many cannot cope with the excessive humidity.

A quick warming of 20° C would need very careful management for the country to cope; without careful and active management the country will descend into chaos before reorganizing itself. Most of the plants won't be able to survive; if there is enough rain, new plants will take their place. Many crops won't make the transition; new crops must be substituted, again if there is enough rain.

Warmer places need more water

As we have seen, Stockholm gets only 531 mm if rain per year, whereas Naples gets about twice that; and yet, Naples does not look wetter than Stockholm, quite the contrary. Algiers on the northern coast of Africa gets just a little more rain per year than Stockholm, but it definitely looks parched compared to the capital of Sweden. That's because warmer climate induces more evaporation, including plant transpiration. Increasing the temperature with an average 10° C while keeping the same amount of rain would transform Sweden into northern Africa, a region where agriculture is possible but quite difficult and anyway very different. Increasing the temperature 20° C while keeping the same amount of rain would transform Sweden into an outright desert.

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Plants by themselves usually handle warmth and moisture very well. In the short term, most of them would thrive.

Over the next few years, there would be massive ecological changes as some plants out-compete others in the new environment.

Your world is going to get devastated by storms, though. If your world is heating up and 1 degree a month your atmosphere is going to be incredibly turbulent. You are going to see Cat 5 hurricanes, tornadoes, the works. Anything that's not bolted to the ground - and a lot of things which are bolted to the ground are going to get uprooted.

Other areas are going to see massive flooding.

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I think it really depends a lot on the lay of the land.
If the rainfall increases a lot then low areas with poor drainage would become bogs/swamps. High, well drained areas would probably thrive.
Annual plants might become perennials, since the warmer winters could keep them from dying off completely. Some of the summer plants might turn into winter plants, if the summer heat is above their threshold.
Crop cycles would change a lot. You'd be able to plant earlier, harvest later, meaning that you could have several growing seasons each year. Depending on the winter temperature, you could potentially grow some crops year round.

The increated rain would help, but likely they'd have to import some plants/seeds from more tropical areas as the temperate/dry loving plants died off.

Mosquitoes and other hell spawn would become a bigger problem since there would be more standing water and less chance of cold killing them off. This could affect cattle.

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A couple of years are not enough for evolution to happens.

Plants which are highly sensitive to environmental conditions would likely largely suffer or even disappear from their original regions. I.e. a cactus or an orchid do not handle well quantities of water outside their comfort zones.

More "relaxed" plants may still thrive or even grow better. But at this point you also need to check how the environmental condition affects the reproduction assistants of the plants:

  • intensive rains may affect the ability of some anemophile plants to spread their pollen
  • bees and insects may suffer from altered climate conditions.

Livestock, depending on plants for foraging, will be affected, especially those relying on open grazing. However, being this aspect influenced by the humans, it can be mitigate by importing new types of plants.

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