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The Science Behind COP26: The IPCC’s ‘Code Red for Humanity’ report

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In 2007, I was in my second year of an undergraduate degree in Environmental Hazards. It was not long after the release of Al Gore’s totemic documentary ‘An Inconvenient Truth’ and I recall lectures at the time discussing the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) which warned thatWarming of the climate system is unequivocaland that it was very likely” caused by human increases in greenhouse gas concentrations.  

There was a strong sense of urgency that global action to curb emissions was required. Climate change then took a back seat as governments around the world scrambled to deal with the 2007-08 financial crisis.

Fourteen years and two further IPCC reports later, it feels somewhat like Groundhog Day. Climate science has progressed significantly, but the key conclusions of the 2007 IPCC report bear a striking resemblance to those published this year:

“It is unequivocal that human influence has warmed the atmosphere, ocean and land.”

IPCC, 2021, AR6 report (emphasis added).

Furthermore, we are again in the midst of another global crisis, this time caused by the COVID-19 pandemic.

All the while, the climate crisis looms large and the concentration of Carbon Dioxide (CO2)in our atmosphere continues its steady upwards march, warming the climate at a rate unprecedented in the last 2000 years. The chart below shows key statements from each IPCC scientific assessment since 1990 alongside the concentration of CO2 in the atmosphere which has continued to increase over the same time period. 

This image summarises key statements from each IPCC scientific assessment report since 1990 plotted against a chart that shows the steady increase in atmospheric carbon dioxide since 1990. It shows that the science has consistently warned about the impact humans are having on the climate. Despite this, carbon dioxide levels have continued to rise.
Data source: IPCC; CO2 data from Mona Loa Observatory, Hawaii (Dr. Pieter Tans, NOAA/GML ( and Dr. Ralph Keeling, Scripps Institution of Oceanography (

A ‘Code Red for Humanity’

Scientists tend to be a cautious bunch. The scientific language of IPCC reports doesn’t lend itself well to punchy headlines. However, the UN Secretary-General António Guterres was not so cautious in communicating the gravity of the latest report:

“Today’s IPCC Working Group 1 report is a code red for humanity.  The alarm bells are deafening, and the evidence is irrefutable: greenhouse‑gas emissions from fossil-fuel burning and deforestation are choking our planet and putting billions of people at immediate risk. Global heating is affecting every region on Earth, with many of the changes becoming irreversible.”

UN Secretary-General António Guterres (emphasis added).

The UN Secretary-General was, in effect, saying what the scientific community is thinking. This is an emergency, and there is no more time to waste.

What are the key findings and what does this mean for Scotland?

The IPCC publishes ‘regional factsheets’ alongside its main report. These factsheets set out some of the expected climate change impacts as predicted by the current scientific evidence. Some of the key impacts for Europe are summarised below.

Increased temperatures

“Regardless of future levels of global warming, temperatures will rise in all European areas at a rate exceeding global mean temperature changes, similar to past observations (high confidence).”

IPCC AR6 Regional Fact Sheet – Europe (emphasis added).

In other words, the emissions we’ve already made will have consequences, regardless of future action to cut emissions. We’re already experiencing rising temperatures in Scotland. Our 10 warmest years on record have all occurred since 1997. If our current mid to high emissions trajectory continues, summers are predicted to be hotter and drier and winters warmer and wetter.  

This chart shows the average annual air temperature in Scotland from 1890 to 2020. The air temperature varies over time but the 7-year moving average shows an increasing trend in temperatures from around 1980 to present. The 10 hottest years are highlighted. All have occurred since 1990.
Data source: Met Office National Climate Information Centre

Winter frost

“The frequency of cold spells and frost days will decrease under all the greenhouse gas emissions scenarios in this report and all time horizons, similar to past observations. (high confidence)”

IPCC AR6 Regional Fact Sheet – Europe (emphasis added)

Fewer cold spells and less frost might sound like a good thing, and in some cases, this is true. Take agriculture for example. Warmer winters lead to less frost damage to crops, longer growing seasons and crop yields. But on the flipside, warmer winters can also have negative impacts such as increased pest activity, crop disease, and the expansion of invasive and non-native species. Crucially, it’s the rate of change that’s of concern and the pressure this may exert on natural systems.

The IPCC report also predicts strong declines in snow cover. This could have an impact on snow sports centres in Scotland which have been estimated to contribute an estimated £30 million to the Scottish economy per year and provide over 600 jobs in rural communities. A recent study analysing historical snow depth and extent on Cairn Gorm found that since 1983 there has been a 10cm reduction in the maximum snow depth and a 10-day decrease in the number of days where shallow snow depths occur (between 2 and 10cm). This trend is predicted to continue with the possibility of some years of very little snow by 2080 at the highest elevations.

This image is a photo of skiers and snowboarders descending a snow covered mountain side on Cairn Gorm in the Scottish Highlands.
Skiers and snowboarders on Cairn Gorm. Scenes like this are predicted to become much rarer by the end of the century (Photo credit: Sandy Stevenson, Flickr).

Increased rainfall

“Observations have a seasonal and regional pattern consistent with projected increase of precipitation in winter in Northern Europe. (…) Extreme precipitation and pluvial [surface water] flooding are projected to increase at global warming levels exceeding 1.5°C in all regions except the Mediterranean. (high confidence)”.

IPCC AR6 Regional Fact Sheet – Europe (emphasis added)

We are already witnessing increased rainfall in Scotland, with an increasing proportion coming from heavy rainfall events. The annual average rainfall in Scotland during the last decade (2010-2019) was 9% wetter than the 1961-1990 average, with winters 19% wetter.

The consequences of such climate change was tragically demonstrated last year when a train derailed near Stonehaven after hitting landslip debris following a heavy rainfall event, killing three people and injuring six others. Future projections also make flash flooding events like those seen in Edinburgh this summer more likely and more frequent.

Sea-level rise

“Regardless of level of global warming, relative sea level will rise in all European areas except the Baltic Sea, at a rate close to or exceeding global mean sea level. Changes are projected to continue beyond 2100. Extreme sea level events will become more frequent and more intense, leading to more coastal flooding. Shorelines along sandy coasts will retreat throughout the 21st century (high confidence).”

IPCC AR6 Regional Fact Sheet – Europe (emphasis added)

Sea levels are rising due to the expansion of water from warmer ocean temperatures and the melting of glaciers, ice caps and ice sheets. Sea-level rise projections based on different emissions pathways known as ‘Representative Concentration Pathways (RCP)’ for towns and cities around Scotland’s coastline and islands are shown in the chart below. Rates of sea-level rise vary due to differences in the rate at which land is still rebounding after being depressed by the immense weight of the vast ice sheet that once covered Scotland.

For example, the chart shows that sea level is projected to rise in Edinburgh by around 0.2 metres (20cm) by the end of the century on a low emissions pathway or half a metre under a high emissions scenario. For Lerwick, Shetland, this is much higher at around half a metre and three-quarters of a metre respectively.

Rising seas are predicted to increase the likelihood and frequency of coastal flooding and lead to increased coastal erosion. The Scottish Government estimates that £400 million of coastal assets will be threatened by 2050.

What does this mean for COP26?

The weight of scientific evidence is now insurmountable, and the implications are stark. In short, global leaders attending COP26 are faced with the challenge of agreeing on binding and ambitious actions that will lead to rapid, transformative change to cut emissions. Anything less will make avoiding dangerous increases in global temperatures unavoidable. 

Looking back at the last 14 years since those undergraduate lectures, it would be easy to feel despair at the lack of progress in cutting global emissions. But a few important distinctions can be made between 2007 and 2021. The science is no longer in dispute, the climate and ecological crisis and ‘Green recovery’ is a top priority for voters and politicians, and children and young people are making their voices heard. This gives some cause for hope for the future prosperity of Scotland and the planet.

Damon Davies, Researcher, SPICe

This blog was updated on 28/10/2021 to “sea level is projected to rise in Edinburgh by around 0.2 metres (20cm) by the end of the century”.