Climate change - is it our fault? Yes it is. Ever wonder how we know? Dr. Chris Derksen, Research Scientist at Environment and Climate Change Canada, explains how scientists are able to measure the effect human activity has had in changing our climate.

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ask a scientist

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Ask a Scientist Intro flips through various images showing the effects of climate change. Host of Ask a Scientist sits in his office and begins the episode.

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Kerbens Boisette (Host, Ask a Scientist, Environment and Climate Change Canada)

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Hey everyone, today’s episode is about climate change. We received an interesting question on twitter about where it comes from.

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Young girl sits in living room and asks her climate change question.

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Néhlia (Gatineau, QC)

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Hi, how do we know climate change is caused by humans?

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Host finishes introduction and hands off to scientist.

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You see, humans are a fascinating species. We create music, art, food, and so much more. But we are also responsible for climate change. How and why is this true? Let's ask one of our climate change experts, Dr. Chris Derksen.

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Scientist sits in home to start responding to the participant’s question.

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So, our question is, how do we know that climate change is caused by human activities?

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Fast paced shot of a busy city street.

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How do we know that climate change is caused by human activities?

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Well, we know the concentration of greenhouse gases like carbon dioxide and methane in the atmosphere are increasing, and the burning of fossil fuels through human activities is the primary driver of this increase.

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Various shots of greenhouse gas emission sources.

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Greenhouse gases
C02 Carbon Dioxide
CH4 Methane

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A higher concentration of greenhouse gases in the atmosphere results in more heat being trapped by the atmosphere, and a warming of surface temperatures.

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Animation shows the evolution of industrial pollution. Animated thermometer rises.

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Chris Derksen (Research Scientist, Environment and Climate Change Canada)

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So, these basic physics of climate change are very well understood, and they are confirmed by very careful measurements of greenhouse gas concentrations and surface temperature that are made around the world. These observations are clear and compelling.
Now, climate models tell us what we can expect from future climate states, but they're also very helpful for understanding historical climate change.

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Climate model shows projected change in surface air temperature from a 21 year time span.

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Projected Change
11 Year Mean
Surface Air Temperature

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And climate model experiments have been run for an idealized 20th century for which we pretend there were no greenhouse gas emissions from human activities.

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Animation of polluted earth transforming into a clean planet. Animated people pop up one by one, happily holding signs advocating for a green planet.

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So essentially, we want to know, what if the industrial revolution never occurred? What if the atmosphere now looked the same as it did in 1850?

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Old footage of industrial factories. Old footage of family hanging out by the beach.

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Well these simulations show no evidence of climate change, no evidence of warming temperatures. So simply put, climate models only simulate the observed climate change if they include human activities, which produce greenhouse gases into the atmosphere.

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Various clips showing the effects of climate change, one by one, pop up to fill the entire screen. A busy city showing cars and people rushing by.

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So, observations play a vital role in tracking climate change, in understanding the rate of change, and climate models are really useful tools for telling us a little bit about why and how climate change has occurred and what we can expect in the future.
So the evidence is clear. Climate change is caused by human activities, and international coordinated action on greenhouse gas emissions are needed to reduce the intensity of climate change in the future.
So thanks for your question, and keep those climate questions coming in.

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Host sits in his office and concludes the episode.

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The industrial revolution, while amazing in itself, definitely did a number on our planet. Thankfully, we have ways to understand our environmental issues using tools like climate models.
Ask your questions and get your answers, here on Ask a Scientist.

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