Local & Extreme Weather

9 minute read

Updated on: 17th May 2020

So far we have discussed temperature increases and sea level rise, both of which are happening at a global scale. But global warming will also cause many changes in local weather patterns, such as increases in the number and intensity of heavy rains, droughts and heatwaves. In this chapter we look at these local changes and extreme weather.

Image of Changes in local weather

Image: Changes in local weather

How will climate change affect precipitation?

As the average global air temperature increases due to climate change, our atmosphere will be able to hold more water vapour. This is because at higher temperatures, water molecules on the ground or on the surface of the sea or lakes have more energy, making it easier for them to escape from liquid water and turn into gas in the atmosphere.

Therefore, in a warmer climate, the atmosphere will contain and release more water, increasing the occurrence of rain, sleet and snow (which are collectively known as precipitation).

Image of Increasing rain with global warming

Image: Increasing rain with global warming

‘Rainfall intensity’ - the amount of rain falling at a given time in a local region - will also increase, so extreme precipitation events (i.e. heavy rain rather than drizzle) will become more likely. Evidence suggests that for every 1°C of global warming, extreme precipitation events could occur 5-10% more often. Therefore, more of the land on Earth will be at risk of flooding.

How will changes in precipitation vary across the globe?

The changes in precipitation are predicted to be uneven. Look at the map below:

Image of Global Precipitation Change

Image: Global Precipitation Change

It shows how the average precipitation for 2081-2100 will be higher or lower than the average precipitation during 1986-2005, if there are no changes or additions to current climate policies. For example, over most parts of the equator it is predicted to rain 0.8 millimetres more per day at the end of this century than it did at the start.

Can you see that some regions will become wetter, others will become drier, and some will hardly change? In part, this is because some parts of the atmosphere will warm more than others, so they will be able to hold more water.

There will also be changes in the flow of air in the atmosphere which will change the ways in which water is distributed across the globe. For example, even less water will be brought to the deserts near the equator and even more will be concentrated in the world’s tropical rainforests.

Overall, land regions far away from the equator will become wetter, whilst land regions closer to the equator will become drier if they are already dry, and wetter if they are already wet!

Image of Drier and Wetter

Image: Drier and Wetter

How will increasing heatwaves affect local weather patterns?

Heatwaves are periods of abnormally hot weather. Almost all parts of the globe have faced an increased number of heatwaves since 1950, breaking multiple temperature records. This is likely to be caused by human activities, and scientists predict that heatwaves will continue to become more common and more extreme as we release more greenhouse gases.

Wildfires increase because plants, dried out from heat and lack of water, are more likely to catch fire. In 2018, 186 thousand hectares of California burned and 85 people died. In the 2019-2020 fire season, an area over 40 times bigger was burned during the Australian bushfires.

It is unclear how heatwaves across the whole planet will change, due to a lack of sufficient data from Africa and South America. However, we do know that Europe, Australia and much of Asia have all experienced more frequent heatwaves since 1950, as have many regions in North America.

How will heatwaves and local changes in precipitation affect droughts?

A drought is a period of unusually dry weather which lasts long enough to affect the water cycle in some way. With climate change causing changes in precipitation, some dry regions of the Earth will become drier, making droughts more likely to happen. Furthermore, in a hotter world, the severity of droughts is likely to increase.

For example, droughts in the Mediterranean and West Africa have become longer and more intense since 1950. If global warming goes beyond 2°C, more droughts are predicted to occur in the Mediterranean, southwestern USA and southern African regions.

This could seriously affect food security - the ability for all people to be able to access enough safe and nutritious food. This is because if the soil dries up, it is harder to grow crops.

Image of Droughts and Food Insecurity

Image: Droughts and Food Insecurity

How reliable are local predictions compared to global predictions?

Scientists create climate models by dividing the surface of Earth and the atmosphere into a grid of large boxes.

Image of Climate Model

Image: Climate Model

This allows scientists to calculate how specific places will be affected by climate change, rather than just predicting changes for the planet as a whole.

Ideally we’d have lots of really small boxes so that we could know the precise impacts of climate change on the weather in every town or field. But we have to compromise; even reducing the size of the boxes by half would require 10 times the computing power to do calculations in the same amount of time!

Image of Accuracy vs Computer Power

Image: Accuracy vs Computer Power

Nope! 32°C is just the average temperature, local variations in temperature are ignored. These variations within each box can be important for feedback effects so modellers are keen to represent them as well as possible.

If a climate modeller only needs to model local effects in a certain region, they can achieve better local predictions by using boxes roughly half the usual size of around 100-300km.

Since they are only modelling one region, the need for large computer power is no longer an issue, despite the smaller boxes. However, this still isn’t completely reliable and depends on data from global models for processes occurring around the region.

Conclusion

We’ve seen how many extreme weather events could impact different parts of the planet and how they are likely to become more frequent as global warming continues. Combined with the other things we’ve learnt throughout this course - such as the risk of tipping points and projected increases in global temperatures and sea levels - we can see how global warming poses a huge risk to human health, food supply, buildings, transport and wildlife. Therefore, it is vital that we slow climate change as much as possible.

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