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A firefighter tries to extinguish the flames as a local resident holds a water hose during a wildfire at Ellinika village on Evia island, about 176 kilometers (110 miles) north of Athens, Greece, Monday, Aug. 9, 2021.

Petros Karadjias/The Associated Press

Climate change is proceeding at a faster pace and producing widespread effects that are more definitively tied to human influence than ever before, according to a new United Nations report from a global team of scientists.

From higher temperatures, to intense rainfall, extreme drought, rising sea levels and thawing permafrost, the resulting portrait makes clear that even in a world where no one knew or suspected the impact of carbon dioxide and other greenhouse gasses, it would be obvious by now that something is seriously amiss with the atmosphere.

The monolithic report, released Monday, is the most comprehensive and strongly worded assessment yet of the present condition and future trajectory of the Earth’s climate. The report effectively lays the factual foundations for international climate talks scheduled to take place this November in Glasgow, Scotland.

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How do we know humans are causing

climate change?

The observed 1°C warming of the atmosphere since

1850 can only be reproduced in computer simulations

that include human influence.

Greenhouse

gasses (human)

Combined (human/

natural causes)

Observations

Aerosols (human)

Natural causes (incl. solar/olcanic)

2.5

Global surface temp. change since 1850 (˚C)

2.0

90% of simulations

fall within shaded areas

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

1850

1900

1950

2000

‘20

THE GLOBE AND MAIL, SOURCE: ipcc

How do we know humans are causing climate change?

The observed 1°C warming of the atmosphere since 1850 can

only be reproduced in computer simulations that include

human influence.

Greenhouse

gasses (human)

Combined (human/

natural causes)

Observations

Aerosols (human)

Natural causes (including solar and volcanic)

Global surface temp. change since 1850 (˚C)

2.5

2.0

90% of simulations

fall within shaded areas

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

1850

1900

1950

2000

‘20

THE GLOBE AND MAIL, SOURCE: ipcc

How do we know humans are causing climate change?

The observed 1°C warming of the atmosphere since 1850 can only be

reproduced in computer simulations that include human influence.

Greenhouse

gasses (human)

Combined (human/

natural causes)

Observations

Aerosols (human)

Natural causes (including solar and volcanic)

2.5

Global surface temp. change since 1850 (˚C)

2.0

90% of simulations

fall within shaded areas

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

1850

1900

1950

2000

2020

THE GLOBE AND MAIL, SOURCE: ipcc

“If there is any further need of proof that climate change is caused by human activities then this is it ... nothing else can explain it,” said Corrine Le Quéré, a Canadian climate scientist and professor at the University of East Anglia in the United Kingdom who served as a coauthor on the previous UN climate assessment in 2013.

Like that earlier assessment, the new report from the Intergovernmental Panel on Climate Change demonstrates that climate change is not a hypothetical future problem but a real world phenomenon that is readily apparent and accelerating in every region of the globe.

But what is different about the latest iteration – which the authors emphasize in the opening lines of their summary for policymakers – is that humans can now be identified, beyond any reasonable scientific doubt, as the primary cause of climate change and therefore the only avenue for addressing an emerging crisis of planetary proportions.

Dr. Le Quéré added that it is imperative that politicians everywhere recognize the urgent need for action to forestall the worst consequences of a rapidly warming world.

“My hope is that the scale of action [that is necessary] will be perceived by world leaders and that people will be prepared to back that,” she said.

Differences in global warming

Higher latitude countries including Canada are seeing

a greater temperature increase overall. Warming is more

apparent near the equator where natural temperature

variations are smaller.

95% of natural variability falls in this range

68% of natural variability falls in this range

Observed temperature

High latitudes (eg. Mid-North America)

2.0

Change in average annual temp. (˚C)

1.5

1.0

0.5

0.0

-0.5

-1.0

1860

1890

1920

1950

1980

2010

Low latitudes (eg. Tropical South America)

2.0

Change in average annual temp. (˚C)

1.5

1.0

0.5

0.0

-0.5

-1.0

1860

1890

1920

1950

1980

2010

THE GLOBE AND MAIL, SOURCE: ipcc

Differences in global warming

Higher latitude countries including Canada are seeing a greater

temperature increase overall. Warming is more apparent near

the equator where natural temperature variations are smaller.

95% of natural variability falls in this range

68% of natural variability falls in this range

Observed temperature

High latitudes (eg. Mid-North America)

Change in average annual temp. (˚C)

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

1860

1890

1920

1950

1980

2010

Low latitudes (eg. Tropical South America)

Change in average annual temp. (˚C)

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

1860

1890

1920

1950

1980

2010

THE GLOBE AND MAIL, SOURCE: ipcc

Differences in global warming

Higher latitude countries including Canada are seeing a greater temperature increase overall.

Warming is more apparent near the equator where natural temperature variations are smaller.

95% of natural variability falls in this range

68% of natural variability falls in this range

Observed temperature

High latitudes (eg. Mid-North America)

2.0

1.5

Change in average annual temp. (˚C)

1.0

0.5

0.0

-0.5

-1.0

1860

1890

1920

1950

1980

2010

Low latitudes (eg. Tropical South America)

2.0

1.5

Change in average annual temp. (˚C)

1.0

0.5

0.0

-0.5

-1.0

1860

1890

1920

1950

1980

2010

THE GLOBE AND MAIL, SOURCE: ipcc

Under the 2015 Paris Agreement, countries are committed to maintaining global warming below 2.0°C over preindustrial levels with a preferred target of 1.5°C in order to avoid some of the most serious consequences associated with climate change for the world’s population.

The report finds that the global average temperature is now 1.1°C warmer than it was in 1850 -1900 – a steep increase relative to anything seen in recorded history. It will likely exceed the 1.5°C threshold in the next 20 years, which is somewhat sooner than previous estimates have suggested. Some of the longterm effects, including sea level rise and Arctic warming, are essentially irreversible and are already altering the planet. For most people, however, the more immediate impacts of climate change will be experienced through increasing occurrences of extreme weather.

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“In many places we are not only able to see the changes but attribute them to human influence – this is particularly true for temperature,” said Xuebin Zhang, a senior research scientist with Environment and Climate Change Canada in Toronto and a lead author on the chapter in the report that deals with extreme weather events.

Those events, including heat waves and heavy rainfall, are projected to become more frequent and more intense as the global temperature rises. For this reason alone, particularly given recent severe floods in Europe and catastrophic fires in western North America and the eastern Mediterranean, the report could receive significantly more public attention than its predecessors.

“The conclusions of this report align with the lived experience of an increasing number of people,” said Rick Smith, president of the Canadian Institute for Climate Choices, a federally funded think tank.

Dr. Smith said that in addition to bringing greater certainty to the scientific underpinnings of climate change, the report coincides with a shift in public perception: Where climate change was formerly regarded as an environmental issue, it is now seen as impinging more directly on human health and wellbeing.

Global warming: the long view

Direct observations and reconstructed temperature

(10 year average) show that Earth is warming rapidly

relative to other times in human history.

2.0˚C

Current warming

is unprecedented

in more than

2,000 years

1.5

Estimated range of

warmest multi-century

period during past 100,000

years (about 6,500 years ago)

1.0

1.0

Observed

0.5

0.2

0.0

-0.5

90% confidence range

-1.0

1

500

1000

1500

1850

2020

THE GLOBE AND MAIL, SOURCE: ipcc

Global warming: the long view

Direct observations and reconstructed temperature

(10 year average) show that Earth is warming rapidly

relative to other times in human history.

2.0˚C

Current warming

is unprecedented

in more than

2,000 years

1.5

Estimated range of

warmest multi-century

period during past 100,000

years (about 6,500 years ago)

1.0

1.0

Observed

0.5

0.2

0.0

-0.5

90% confidence range

-1.0

1

500

1000

1500

1850

2020

THE GLOBE AND MAIL, SOURCE: ipcc

Global warming: the long view

Direct observations and reconstructed temperature (10 year average) show

that Earth is warming rapidly relative to other times in human history.

2.0˚C

Current warming

is unprecedented

in more than

2,000 years

1.5

Estimated range of

warmest multi-century

period during past 100,000

years (about 6,500 years ago)

1.0

1.0

Observed

0.5

0.2

0.0

-0.5

90% confidence range

-1.0

1

500

1000

1500

1850

2020

THE GLOBE AND MAIL, SOURCE: ipcc

The report is the first of three documents designed to lay out the best available knowledge about climate change. A second report on climate impacts and a third on mitigation strategies are set for release in the first half of next year, with a final synthesis of all three reports to come in September of 2022. Together the reports comprise the sixth global assessment of the state of the world’s climate organized by the intergovernmental panel since its creation in 1988.

It is Monday’s report, however, that sets the tone and scope for those that follow because it is tied to the physical behaviour of the atmosphere and its multiple cycles and interactions with other major components of the climate system such as the oceans, polar ice sheets and forests. It does not consist of newly gathered data but rather distills the peer-reviewed work of thousands of scientists published since the fifth assessment was completed. Last week it received the final approval of the panel’s 195 member nations, including Canada.

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“It draws together a huge body of science that has accumulated over the past eight years and puts it into context,” said Gregory Flato, a vice-chairman of the international team that behind the report and a senior research scientist at the Canadian Centre for Climate Modelling and Analysis in Victoria, B.C.

The Canadian centre is one of several worldwide that run high-powered computer simulations showing how the global climate is likely to evolve in the future under different emissions scenarios. The centre is also involved in the development of climate projections for Canada. One of the changes in the new report is a beefed up section on regional climate, including an online atlas meant to help policy makers and the public understand what climate change will mean for them.

Dr. Flato noted that the greater certainty in the language adopted by the report’s authors can be chalked up to all the data that have accumulated since the previous assessment as the magnitude of climate change has grown, as well the increasing power of computer models to capture the extent to which human influence is playing a role in the climate.

Where Canada is warming most

While the temperature at any location varies through

the day and across the seasons, the average annual

temperature has been rising everywhere in Canada,

mostly dramatically in the northwest.

Increase in average annual temperature (1948-2016)

˚C

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

THE GLOBE AND MAIL

SOURCE: X. Zhang/ECCC

Where Canada is warming most

While the temperature at any location varies through the day

and across the seasons, the average annual temperature has

been rising everywhere in Canada, mostly dramatically

in the northwest.

Increase in average annual temperature (1948-2016)

˚C

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

THE GLOBE AND MAIL

SOURCE: X. Zhang/ECCC

Where Canada is warming most

While the temperature at any location varies through the day and across

the seasons, the average annual temperature has been rising everywhere

in Canada, mostly dramatically in the northwest.

Increase in average annual temperature (1948-2016)

˚C

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

THE GLOBE AND MAIL

SOURCE: X. Zhang/ECCC

The latest evidence shows with improved clarity just how far the global temperature has diverged from the range of natural variability. Overall, a net warming due to greenhouse gas emissions has become the dominant factor in that change. When combined with the cooling effect of pollutants known as aerosols and non-human factors including solar variations, volcanic eruptions and ocean cycles, the expected direction of the climate closely matches what has been observed.

John Fyfe, another senior researcher at the Canadian centre and a lead author on the chapter of the report related to future climate scenarios, said that scientists have benefited from building geological and chemical evidence that independently reveals how Earth’s climate has responded to changes in carbon dioxide levels during prehistoric times – a variable known as climate sensitivity.

One of the challenges leading up to the report was the realization that some models, including Canada’s, are thought to be overestimating climate sensitivity, possibly as a side effect of improvements to other aspects of their calculations. Dr. Fyfe said specific disagreements between climate models have tended to balance out in the process of combining results from multiple centres.

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“What’s really important to understand is that knowledge is always evolving,” said Linda Mortsch, a member of the University of Waterloo’s Interdisciplinary Centre on Climate Change and a lead author on the second instalment of the IPCC assessment expected in February.

“Scientists are very conservative and they have a very high bar in terms of what they accept as evidence or how strong they will talk about something,” she added. “This is the evolution that you’re seeing here.”

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