Topic: Climate Change

IPCC 2021 – Changing Climate Zones

Post date 5 January 2022

According to the IPCC report for Policymakers “Changes in the land biosphere since 1970 are consistent with global warming: climate zones have shifted poleward in both hemispheres, and the growing season has on average lengthened by up to two days per decade since the 1950s North of the Tropic of Cancer”¹

Complete the table below on the positives and negatives of the changes described above

Summary of changes to the Biosphere from the report²

Warming contributed to an overall spring advancement in the Northern Hemisphere.
There are increases in the length of the thermal growing season over much of the land surface since at least the mid-20th century. The thermal growing season is the length of time in a calendar year when temperatures are warm enough for agricultural activity.
Over the Northern Hemisphere as a whole, an increase of about 2.0 days per decade is evident for 1951–2018 with slightly larger increases north of 45°N.
Over North America, a rise of about 1.3 days per decade is apparent in the United States for 1900–2014 with larger increases after 1980.
Growing season length in China increased by at least 1.0 days per decade since 1960 .
Peak bloom dates for cherry blossoms in Kyoto, Japan have occurred progressively earlier in the growing season in recent decades. In 2021, peak bloom was reached on 26 March, the earliest since the Japan Meteorological Agency started collecting the data in 1953 and 10 days ahead of the 30-year average.³
Grape harvest dates in Beaune, France have also been earlier. Using harvest data for Beaune stretching back nearly 700 years it has been noted that from 1354 to 1987, grapes were on average picked from 28 September whereas during the last 31-year-long period of rapid warming from 1988 to 2018, harvests began 13 days earlier.⁴

2. Map the changes listed above on the appropriate regions on the world map below:

Source – https://equal-earth.com/

Changes in dates for various plants, crops and regions

Image source: Adjusted from IPCC ¹

Add straight lines of best fit to each graph.
What has happened to the date of the grape harvest in France? Use data to describe the change.
Which graph shows the greatest change?
Which graph shows the smallest change?
How might these changes affect insect, bird and land animals? You could research these and consider migration, harvesting, hibernation and flowering times.
How might these changes affect farmers and food supply?

The change in growing season in the USA

Study the graph⁵ below:

Complete the table below using information from the graph. Use the nearest WHOLE NUMBER available.

Explain which location has the greatest change in its growing season. Use data from the table above in your response.
Make a list of advantages that this shift in growing season will bring to the USA.

Sources:
1. IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press. P.7. Accessed 28^th November 2021 at Sixth Assessment Report (ipcc.ch)
2. IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press. P.517. Accessed 28^th November 2021 at Sixth Assessment Report (ipcc.ch)
3. Associated Press (author unknown), 2021. Climate crisis ‘likely cause’ of early cherry blossom in Japan. [online] the Guardian. Available at: https://www.theguardian.com/world/2021/mar/30/climate-crisis-likely-cause-of-early-cherry-blossom-in-japan [Accessed 28 November 2021]
4. Mercer, C., 2021. Burgundy harvests getting earlier as vineyards heat up, says study – Decanter. [online] Decanter. Available at: https://www.decanter.com/wine-news/burgundy-harvests-earlier-study-423807/ [Accessed 28 November 2021].
5. US EPA. 2021. Climate Change Indicators: Length of Growing Season | US EPA. [online] Available at: https://www.epa.gov/climate-indicators/climate-change-indicators-length-growing-season [Accessed 28 November 2021].

IPCC 2021 – Which Regions have been affected the most by climate change?

Post date 5 January 2022

“A.3 Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since AR5”¹

Consider the three following maps with your students, or alternatively focus in on one of the maps.

Heavy Precipitation

“A.3.2 The frequency and intensity of heavy precipitation events have increased since the 1950s over most land area for which observational data are sufficient for trend analysis (high confidence), and human-induced climate change is likely the main driver. Human-induced climate change has contributed to increases in agricultural and ecological droughts in some regions due to increased land evapotranspiration (medium confidence).”¹

Source: Adjusted from IPCC ¹

Study carefully the map above which shows an assessment of the observed change in heavy precipitation across the globe.
How many of the regions showing on the map have experienced an increase in heavy precipitation?
How many of the regions shown on the map have experienced a decrease in heavy precipitation?
What is the situation in the region where you live with regards to changes in heavy precipitation?
Identify the region where there is high confidence in the human contribution to the observed change.
Use TEA (Trend, Evidence, Anomoly) to describe the patterns shown on the map above. Which regions have had an increase in observed heavy precipitation? Which regions have limited evidence?
Suggest what impacts an increase in heavy precipitation might have.
Look closely at the areas that have limited data and/or literature. Can you suggest reasons why these areas have limited data and literature in relation to heavy precipitation?

Hot Extremes

“A.3.1 It is virtually certain that hot extremes (including heatwaves) have become more frequent and more intense across most land regions since the 1950s, while cold extremes (including cold waves) have become less frequent and less severe, with high confidence that human-induced climate change is the main driver14 of these changes. Some recent hot extremes observed over the past decade would have been extremely unlikely to occur without human influence on the climate system. Marine heatwaves have approximately doubled in frequency since the 1980s (high confidence), and human influence has very likely contributed to most of them since at least 2006.”¹

Source: Adjusted from IPCC ¹

The IPCC define an extreme weather event as “an event that is rare at a particular place and time of year. Definitions of rare vary, but an extreme weather event would normally be as rare as or rarer” than the top or bottom 10% of observed events. Therefore, for hot extremes these would be periods where temperatures are in the top 10% for that region.¹

Study the map above carefully which shows an assessment of the observed change in hot extremes across the globe.
How many of the regions showing on the map have experienced an increase in hot extremes?
How many of the regions shown on the map have experienced a decrease in hot extremes?
What is the situation in the region where you live with regards to changes in hot extremes?
Identify the region where there is high confidence in the human contribution to the observed change.
Describe the patterns shown in the regions that have had an increase in observed hot extremes.
Suggest what impacts an increase in hot extremes might have.
Look closely at the areas that have limited data and/or literature on both the hot extremes and heavy precipitation maps. There are more regions with limited data on the heavy precipitation map. Can you suggest reasons why?

Agricultural and Ecological Drought

“A.3.5 Human influence has likely increased the chance of compound extreme events18 since the 1950s. This includes increases in the frequency of concurrent heatwaves and droughts on the global scale (high confidence)”¹

Image source: Adjusted from IPCC ¹

The IPCC define Drought as “A period of abnormally dry weather long enough to cause a serious hydrological (water) imbalance.”¹ This would mean that the amount of rain that falls is not sufficient to meet agricultural (farming) or ecological (the plants and animals in a region) needs and during the growing season impinges on crop production or ecosystem function.

How many of the regions showing on the map have experienced an increase in agricultural and ecological drought?
How many of the regions shown on the map have experienced a decrease in agricultural and ecological drought?
Identify the two regions where there is medium confidence in the human contribution to the observed change.
What is the situation in the region where you live with regards to changes in agricultural and ecological drought?
Describe the patterns shown in the regions that have had an increase in observed agricultural and ecological drought.
Suggest what impacts an increase in agricultural and ecological drought might have.
Look closely at the areas that have limited data and/or literature. Can you suggest reasons why these areas have limited data and literature in relation to agricultural and ecological drought?

Overview – Which Regions have been Affected the Most?

Source: Adjusted from IPCC ¹

Using the graphic above identify three places but are affected negatively by all three situations [hot extremes, heavy precipitation, and agricultural and ecological drought]
Using the graphic identify an area that that is affected by fewest of the situations?
Which areas on the map should be a priority for further research into the effects of climate change? Explain your answer.
Which of the three situations have affected most regions of the world? Use evidence from the maps to support your answer.
Write a letter to your local MP, use evidence from the graphic to justify the need for action on climate change. You should focus upon the urgent need for action and how that can be implemented (done) locally.

Geographical information systems activity

Visit the website below, it is the Intergovernmental Panel on Climate Change’s Interactive Atlas. IPCC WGI Interactive Atlas Click on the regional information button, it will bring up an interactive map. Complete the table below using information from the map. You will need to use the menu tools above the map, changing the variable and scenario. Complete this for the Near Term. If you finish, you could repeat for the Long Term on a new sheet and then compare results.

Overall what does the table and map show you about global climates in the future?

Note

SSP1-2.6: Global CO₂ emissions are cut severely, but not as fast, reaching net-zero after 2050. Temperatures stabilize around 1.8°C higher by the end of the century.
SSP5-8.5: Current CO₂ emissions levels roughly double by 2050. The global economy grows quickly, but this growth is fuelled by exploiting fossil fuels and energy-intensive lifestyles. By 2100, the average global temperature is a scorching 4.4°C higher.

Sources:

IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press. P.11. Accessed 28^th November 2021 at Sixth Assessment Report (ipcc.ch)

IPCC 2021 – Urban Regions

Post date 16 December 2021

Climate change and urban areas

C.2.6 Cities intensify human-induced warming locally, and further urbanization together with more frequent hot extremes will increase the severity of heatwaves. Urbanization also increases mean and heavy precipitation over and/or downwind of cities and resulting runoff intensity.¹

The table below shows the efficiency of various factors at warming up or cooling down neighbourhoods of 3 urban areas. Overall, cities tend to be warmer than their surroundings. This is called the ‘urban heat island’ effect. Cities and urban areas tend to be warmer due to extra warming caused by human activities such as industrial processes, but also because urban surfaces tend to be darker coloured and drier than rural surfaces.

Recall that a positive figure represents a temperature rise and a negative figure represents a temperature decrease.

Calculate the difference between the worst- and best-case scenarios.
Which factor has the greatest variability between the best and worst case scenarios?

Which factor has the smallest variability between the best and worst case scenarios?
Using the average change data, how much additional temperature change could there be in cities that have no sources of water & no vegetation?

Complete the graph by adding the average change to city areas temperature for each of the five factors shown in the table.
Which of the five factors shown has the biggest warming impact in cities?
Which of the five factors shown has the biggest cooling impact on a city?

Image source: Google maps

Which of the following locations would be most likely to….
Feel cooler during a summer heatwave?
Feel too hot in a summer heatwave?
Have people wearing shorts and a t-shirt in summer?
Observe the tarmac on the roads melt in a summer heatwave?

According to the IPCC in the future:

Further urbanization will amplify the projected air temperature change in cities regardless of the characteristics of the background climate, resulting in a warming on minimum temperatures that could be as large as the global warming itself.
Compared to present day, large implications are expected from the combination of future urban development and more frequent occurrence of extreme climate events, such as heatwaves, with more hot days and warm nights adding to heat stress in cities.

Using these statements, what are the two factors that will cause temperatures to rise in urban areas?

Imagine that you could redesign the city to limit the effects of climate change. Make a list of all of the things that you could do to reduce the impact of climate change on your chosen city. Next, consider the strengths and weaknesses of all of those options. You might want to consider using a table like the one below;

Using the urban areas fact sheet

Read very carefully through the fact sheet from the IPCC, about the impact of climate change on urban areas. You can access it here – Urban Areas fact sheet (ipcc.ch)
Explain why urban areas can influence the temperatures locally:
Suggest how urbanisation might affect the water cycle within urban areas. Make a list below;

Source: IPCC, 2021²

Using the map above, identify;

The city with the greatest increase in temperatures
The city with the smallest increase in temperatures
A city where the temperature has not changed
The city where urban effects have caused the largest relative share of total warming
The city where urban effects have caused the smallest relative share of total warming
The areas of the world but have heated the most between 1950 and 2018
An area of the world which has experienced cooling in the same time period
Considering what you have already learned, suggest reasons why some cities have warmed more than others

Source: IPCC, 2021 ²

Using the graph from Japan answer the following questions;

In 1900 which area was the warmest?
In the year 2000 which area was the warmest?
Calculate the temperature difference between the urban and rural areas of Japan in 1900.
Calculate the temperature difference between the urban and rural areas of Japan in the year 2000.
In which year did urban temperatures surpass rural temperatures for the first time?
Suggest reasons why Tokyo is now significantly warmer than Choshi
Describe the general patterns on the graph.

According to the IPCC:

The difference in observed warming trends between cities and their surroundings can partly be attributed to urbanisation
Urbanisation has exacerbated changes in temperature extremes in cities, in particular for night time extremes.

One study examining the 2003 heat wave in Europe that killed upward of 70,000 people found that night-time temperatures were a key indicator of the health risk from high temperatures. There’s also research that shows high night-time temperatures disrupt sleep. Without relief from the heat, the stresses on the body mount.

While it may cool off after the sun sets during a heat wave, it may not cool off enough for people who have been exposed to high temperatures all day. That leads to a higher cumulative exposure to heat.

Extreme heat is one of the deadliest weather phenomena in the world. There are direct health effects like heat stroke, (when body temperature rises above 40C, leading to organ failure) and heat exhaustion.

Prolonged periods of high temperatures cause cardiac and respiratory disease leading to excess deaths, particularly in older people.

Simplify the information above into the flow chart below:

Explain why the fact that urbanisation has increased night time extremes of temperature could pose health problems for people who live in cities.

Sources

IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press. In Press. P.34. Accessed 28^th November 2021 at Sixth Assessment Report (ipcc.ch)
IPCC.ch. 2021. Regional fact sheet – Urban Areas. [online] Available at: https://www.ipcc.ch/report/ar6/wg1/downloads/factsheets/IPCC_AR6_WGI_Regional_Fact_Sheet_Urban_areas.pdf [Accessed 5 December 2021].

Key Stage 3 – Trees and Carbon Capture

Post date 9 December 2021

Resource produced in collaboration with MEI

Brief overview of session ‘logic’

Why trees are good
How much carbon do trees capture and store?
How does the amount of carbon captured and stored by a tree change during its lifecycle?

Mathematical opportunities offered

Interpretation of data, statistics, graphs, infographics in context
Critiquing graphs
Analysing and comparing data in order to develop and present a conclusion
Making assumptions
Making predictions
Reading scale

Download the resources

Key Stage 3 – Trees for Net Zero (Extended Resource)

Post date 9 December 2021

Resource produced in collaboration with MEI

Brief overview of session ‘logic’

Why trees are good
People are planting trees – estimates around what the numbers look like in terms of land use
Some companies encourage you to offset flights by planting trees – how many trees for one flight?
How much carbon do trees capture and store?
How does the amount of carbon captured and stored by a tree change during its lifecycle?
What happens to that carbon when a tree dies?
Can you plant a tree to offset a flight?
What is Net Zero?

Mathematical opportunities offered

Estimation and proportional reasoning
Developing a sense of scale of large numbers
Interpretation of data, statistics, graphs, infographics in context
Critiquing graphs
Analysing and comparing data in order to develop and present a conclusion
Making assumptions
Making predictions
Reading scales

Download the resources

Core Maths – Trees and Carbon Capture

Post date 9 December 2021

Resource produced in collaboration with MEI

Brief overview of session ‘logic’

Why trees are good
How much carbon do trees sequester?
How does the amount of carbon sequestered by a tree change during its lifecycle?

Mathematical opportunities offered

Interpretation of data, statistics, graphs, infographics in context
Critiquing graphs
Analysing and comparing data in order to develop and present a conclusion
Making assumptions
Making predictions
Reading scales

Download the resources

Trees for Net Zero (Extended Resource)

Post date 9 December 2021

Sunlight in the green forest, spring time

Resource produced in collaboration with MEI

Brief overview of session ‘logic’

Why trees are good
People are planting trees – estimates around what the numbers look like in terms of land use
Some companies encourage you to offset flights by planting trees – how many trees for one flight?
How much carbon do trees sequester?
How does the amount of carbon sequestered by a tree change during its lifecycle?
What happens to that carbon when a tree dies?
Can you plant a tree to offset a flight?
What is Net Zero?
Can trees be used to achieve Net Zero?

Mathematical opportunities offered

Estimation and proportional reasoning
Developing a sense of scale of large numbers
Converting between m² and km²
Interpretation of data, statistics, graphs, infographics in context
Critiquing graphs
Analysing and comparing data in order to develop and present a conclusion
Making assumptions
Making predictions
Reading scales

Download the resources

How will water circulation and flooding change?

Post date 6 December 2021

This resource links to Figure 11.12 in the IPCC report of 2021. The aim of this resource is to answer the question how will the flow of water around the world be altered with climate change?

It was written with the Royal Geographical Society with IBG.

Circulation

The global atmospheric circulation is described by the Met Office as ‘the world-wide system of winds by which the necessary transport of heat from tropical to polar latitudes is accomplished’. Figure 1 shows the different cells of this global system, in Idealized Earth and Actual Earth projections.

Due to changes in our climate, there will be both small-scale and large-scale changes to the flow of water around the world in the twenty-first century.

The central world map of Figure 8.21 in chapter 8 of the IPCC report shows the effect of 3°C of global warming on mean P-E (precipitation minus evaporation) compared to pre-industrial levels (1850-1900). Describe the anticipated changes to mean P-E across the globe with such projected change. Reference specific regions in your answer.

Using Figure 2 in Appendix A, copy the choropleth colour coding to show the changes to global precipitation for:

a) +0.6 mm to 1 mm increase.

b) -0.6 mm to -1 mm decrease.

Add the Tropical rain belt onto Figure 2, which is shown in red on the original figure.

There are 5 anticipated changes to large-scale water circulation. They are the poleward expansion of the Hadley cells, the poleward migration of storm tracks, the narrowing and strengthening of the Intertropical Convergence (ITCZ) core, a regional shift in the ITCZ, and a weaker Walker circulation (for reference watch the MetLink video An Introduction to Atmospheric Circulation and read https://en.wikipedia.org/wiki/Walker_circulation). Add these notes to Figure 2.

There are multiple atmospheric triggers for changes to the water cycle, termed climate drivers. Figure 3 in Appendix B shows how an increase in precipitation, solar radiation, temperature, wind, and carbon dioxide (CO₂) and a decrease in humidity can influence the water cycle. The diagram flows down to illustrate the outcome on water availability and drought.

Precipitation, one of the climatic drivers

Precipitation has increased steadily over Eurasia, most of North America, south-eastern South America, and north-western Australia. Whilst in Africa, eastern Australia, the Mediterranean region, the Middle East, and parts of East Asia, central South America, and the Canadian Pacific coast it has decreased. Records from 1910 onwards show Scandinavia, north-west Russia, the UK, and Iceland have all experienced increased precipitation trends. The amount of, frequency, and intensity of precipitation is forecast to continue to increase for these areas, which will worsen the severity of flooding. Across Europe there has been a reduction in snowfall, an important component in precipitation, in high latitude and mountain watersheds. Per decade, there has been a reduction of 0.52 million km² of annual mean potential snowfall over Northern Europe, with the greatest loss occurring in the Alps.

Runoff, streamflow, and flooding effect

There have been substantial changes to runoff, streamflow, and flooding around the world. Although there are no significant global trends many human-induced drivers of change have been identified and linked to changes in the flow of water. Examples include decreasing runoff in the dry season in the Peruvian Amazon, a decline in streamflow in the Colorado River, and earlier snowmelt in Northern Europe. As a result, in the UK, there will continue to be problems over increased water availability and streamflow during winter, and a worsening decrease in water availability and streamflow during the summer months. These changes are caused by the difference between winter flooding, which occurs from storm precipitation falling on already waterlogged ground, and summer flooding, when precipitation falls on ground that has been baked hard by the Sun. These scenarios have been compounded by dam construction and water withdrawal, land use and land cover change, all leading to alterations of seasonality, amount, and variability of river discharge, especially in human-dominated small catchments.

Climate change is increasing the risk of both flooding and drought in the UK with flooding now being the most common form of natural disaster. The risk of flooding is increasing due to the anthropogenic drivers of climate change. Quite simply this is because, as the atmosphere warms, there is more evaporation from the surface and more condensation of water vapour into cloud droplets in the atmosphere. Intense precipitation will remain the main cause of flooding. However, there are other factors (such as local topography and geology, for example). In 2017 research by the Met Office found that climate change means there is a high chance of exceeding the observed record monthly rainfall totals in many regions of the UK. Further analysis in 2020 (again by the Met Office) shows that, on average, for the decade 2010 to 2019, UK summers were 13% wetter, and winters 12% wetter, than in the period 1961 to 1990. 7 of the 11 wettest years since records began (in 1862) in the UK have occurred since 1998. The five wettest winters have been from 1990 onwards. Overall, in the UK there is a trend towards wetter winters and drier summers.

Further work

NASA Storms are Getting Stronger

LSE How is climate change affecting river and surface water flooding in the UK?

The Met Office UK extreme events – Heavy rainfall and floods

Sky News Climate change will cause more floods and droughts and England must become resilient, Environment Agency warns

Exam-style question

Using all the work you have completed answer the final question below.

Answer the question: assess whether global flooding will become more severe or more frequent as a result of climate change? This means you must consider the different arguments, likelihoods, and levels of certainty, after weighing them up, to come to a conclusion.

Appendix A

Large Scale Circulation projected changes and their effect on the water cycle

Figure 2 circulation projected change maps © freeusandworldmaps.com arrows © cliparts.co and getdrawing.com

Appendix B

Figure 3 climate drivers © The IPCC report

Answers

The intertropical convergence zone will predominately see an increase in precipitation with 0.8 to 1 mm/d increase across the Pacific Ocean (with some variability near the Central American coast). In the rest of the tropics, both north and south, there will be a reduction in P-E balance with less precipitation over all major oceans within the subtropical boundaries. This is described as a future ‘drying tendency’ on the edges of the ITCZ. In the upper latitude the Barents Sea will also become drier as the P-E balance changes in the Russian Arctic, between Novaya Zemlya and Svalbard. On land much of climate over the South American Amazon will also continue to dry. In contrast Alaska in North America and the Congo basin in Sub-Saharan Africa will see an increase in P-E.
As instructed.
As instructed.
Under a climate change 3° warming scenario the Hadley cell will move northwards away from the current 0° to 30° latitude (N and S). This will lead to the expansion of the subtropical dry zones outwards and away from the tropics. Equally there will be a poleward migration of storm tracks which will lead to stronger storms as they will feed off extra latent heat. Abnormally high sea surface temperatures, in the Atlantic for example, will intensified storms throughout the twenty-first century with associated storm surges being exacerbated by rising sea levels. It is also believed extra water vapor in the atmosphere will make storms wetter. In the future, the ITCZ will narrow, particularly over the Pacific, causing lower latitude subtropical jets to become unstable baroclinically (in temperature and pressure). This will allow midlatitude eddies (circular movements of air) to spread further equatorward leading to more precipitation in the ITCZ core region. The Walker Circulation has undergone a strengthening in the Pacific, thought to be caused by either internal variability or a response to greenhouse gas emissions. The altered circulation pattern is associated with other global changes in the water cycle over regions like the Maritime Continent, South America and Africa.

How often will a heatwave hit the UK?

Post date 6 December 2021

This resource links to Figure 11.12 in the IPCC report of 2021. The aim of this resource is to answer the question how often will a heatwave hit the UK?

It was written with the Royal Geographical Society with IBG.

Box and whisker plots

Figure 11.12 (see Appendix B) is a box and whisker plot. The graph highlights that extreme temperature events are forecast to increase in the twenty-first century. Extreme temperature events are defined as the daily maximum temperatures that were exceeded once during a 10-year (or 50-year) period.

The dataset for Figure 11.12 is from the paper Changes in Annual Extremes of Daily Temperature and Precipitation in CMIP6 Models by Li et al., 2020. An extract of the data is shown below in Table 1 in Appendix A. The numbers in parenthesis ( ) and square brackets [ ] show respectively the central 66% and 90% uncertainty ranges of the estimated changes in annual maximum temperature, from identified warming level ‘windows’.

The warming of annual maximum temperature events is more uniform over land and increases linearly with global warming. There is high confidence that the magnitude of temperatures extremes will continue to increase more strongly than global mean temperature.

Figure 1 the European heatwave of 2021, heat is becoming more extreme and more frequent © University of Maine

The temperature at which an event is classed as a hot extreme is going up (faster than the mean temperature). In the mid-latitudes (between 30° and 60° north and south) the strongest warming is expected in the warm season, with an increase of up to 3°C for 1.5°C of global warming. This has led to events such as the ‘merciless’ temperature spike in Russia, and the ‘heat dome’ over North America in June 2021. The highest increase of temperature in the ‘hottest days’ is projected for some mid-latitude countries and semi-arid regions, such as in North America.

The frequency with which hot events occur is also going up. Study Table 1 in Appendix A. Using Relative frequency change for a 1.5°C, 2°C and a 4°C future, draw a box and whisker plot for global land, with 90% uncertainty ranges. Use the following steps to draw your graph.

a. Draw an x axis and label Global warming above 1850-1900 (°C).

b. Draw the y axis and label Relative frequency change (for one in a 50-year events).

c. Identify the median (the middle) of the data set (which is given to you).

d. Use the 66% uncertainty data (parenthesis brackets) for each box plot.

e. Use the 90% uncertainty data [square bracket] for the whiskers.

In Europe the evidence predicts an increase in the frequency and intensity of hot extremes (warm days, warm nights, heat waves) and, in reverse, a decrease in the frequency and intensity of cold extremes. Heat wave increases will be greater over the south Mediterranean and Scandinavia with southern European cities expected to suffer the biggest increases in maximum heat wave temperatures.

2. Why do cities experience extreme heat more frequently?

3. Now repeat the same activity, graphing Relative frequency change, for the ocean dataset.

Whilst heatwaves will increase across Europe and in the UK, there will still be extreme cold in the future. It is a common misconception to think that, as the climate changes, we will only experience warm weather and extreme heat in the twenty-first century. In fact, the climate distribution will change. Extreme cold will still happen, just less frequently. Figure 3 below illustrates this misconception with a probability curve showing climate likelihood and temperature and, underneath, the change from our previous climate to a warmer one. Both the the threshold temperature for an event to be considered extreme, and the frequency of high temperatures, rise in a warming climate.