When I talk with people who are skeptical about climate change science, I’m often asked: “I know global warming is happening, but how do we know humans are causing the change?”
Source: U.S. Government
- We know that carbon dioxide is the reason the Earth is warming.
- We know that humans are sending huge amounts of carbon pollution into the atmosphere.
More than a century ago, scientists figured out that carbon dioxide and other greenhouse gases trap heat. Since then, we’ve identified many lines of evidence that confirm our planet is warming because of carbon dioxide and the greenhouse effect it produces. Plus, we have evidence that warming can’t be attributed to other factors, like the sun. Solar activity has actually decreased in recent decades.
But how do we know we humans are behind the major increases in carbon dioxide? We’ve left many “fingerprints” that show this is the case.
Since the industrial revolution (the period when humans began intensely burning fossil fuels), levels of carbon dioxide in the atmosphere have increased by about 40%. During this same period, the ocean has become about 30% more acidic due to increased carbon dioxide dissolved in its waters. (The amount of carbon dioxide taken in by the upper layer of the ocean is increasing by about 2 billion tons a year!)
But this is no surprise. We’re emitting carbon dioxide through the burning of fossil fuels faster than the earth can absorb it. And we have the ability to actually show that the excess carbon dioxide in our atmosphere and oceans is coming from fossil fuels, as opposed to natural sources like volcanoes.
When burned, fossil fuels combine with oxygen to produce energy and chemical byproducts like carbon dioxide. According to this recipe, as carbon dioxide is produced, oxygen is lost. Just as we might predict based on this chemistry, we’re observing oxygen levels decrease in our atmosphere as carbon dioxide increases. This is a sign that carbon dioxide levels are increasing because we’re burning fossil fuels.
There’s more. Did you know that the carbon dioxide that comes from fossil fuels can be distinguished from other types of carbon dioxide? It tends to be a bit lighter. So analyses (looking at the carbon dioxide in air samples and the carbon stored in coral reefs) can pick out that the lighter type from fossil fuels is the kind of carbon dioxide that’s increasing.
For an additional illustration of these two human fingerprints, check out this excellent snippet from Earth: The Operators’ Manual. In it, geologist Richard Alley examines the evidence and concludes that the increase in carbon dioxide “is coming from our fossil fuels. It’s us.”
Courtesy of Earth: The Operators’ Manual. Check out the full video here.
klem
November 11th
““I know global warming is happening, but how do we know humans are causing the change?”
Its just because man, its like you can feel it in your bones man. Its real, like when it snows in the winter, that’s like climate change man.
Yea.
Jan
November 12th
I am always baffled by people who seem to have this mindset that unless they know humans are causing this they don’t have to work for sustainable solutions. When you see the lower level of the atmosphere warming but not the upper atmosphere as we have seen, that is a clue. Nighttime temperatures that continue to be warm are a clue as well. Look at CO2/heat charts form Mauna Loa as well. Just understanding the changes to the hydrologic cycle we are now seeing is a clue. But again, this prerequisite some have that they simply will not understand what stewardship to this planet is all about because they now use anthropogenic global warming as their litmus test to sit out life is unrealistic and irresponsible. The health and environmental damage done by fossil fuels alone and the harbinger of peak oil should be enough of a call to them to understand just where we sit as a species if we keep ignoring this.
John Harding
November 13th
Here in Australia people care more about driving a faster more luxurious car or living in a bigger house and will not accept anyone telling them that they have to pay a bit more for anything. We refuse to believe in anything that might reduce our lifestyle or make us pay a bit more, hence a country of climate change deniers.
klem
November 14th
I am always baffled by people who seem to have this mindset that deep down inside they hope and dream that humans are causing this, it’s like some kind of collective self loathing. And no matter what lame clues they find, they interpret everything to human activity as long as its bad. If its interpreted to be good, its nature.
klem
November 15th
“We refuse to believe in anything that might reduce our lifestyle or make us pay a bit more, hence a country of climate change deniers.”
Then how is it you people have agreed to pay a carbon tax, at a carbon price twice the rate paid in the EU?
If your country is full of deniers, then Gillard will get the boot at the next election. Something tells me Gillard will be re elected, and the carbon tax will be the reason.
MrCannuckistan
November 19th
First of all, I disagree with the first statement. We can speculate or hypothesize that CO2 is causing the planet to warm but we cannot prove it, yet. For every piece of evidence confirming this connection there is a corresponding piece of evidence that contradicts the theory.
Secondly, I take exception to the characterization of CO2 (and methane?) as a pollutant. This implies that everything that breathes in oxygen and breathes out CO2 is a scourge on this planet that needs to be dealt with.
The current Holocene epoch has been going on for over 10,000 years and, for the most part, we have 150 years of relatively accurate records. To claim we know enough about the bounds of our climate to formulate a conclusion moving forward is utterly absurd and highly arrogant of us.
That would be like taking the most recent 150 days out of a person’s life and trying to portray an accurate view of their 80 years on this planet.
MsConcerned
December 12th
Climate change is not just about it getting hotter, it is about more extreme weather patterns. Are there not more and more severe hurricanes? That is just one example. It snowed in my little corner of the world for Halloween. That has never happened in the history recorded here. Change is happening. Whether we caused it a lot or a little is irrelevant. Not dealing with the fact that it is changing is irresponsible. Not all who exhale are scourges to the environment. Planet earth was and always will be about a balance of all elements. Can we honestly say that we as a global community have been balancing our use of elements for the better of the planet?
As for the previous comment about taking 150 days of a person’s life to portray an accurate view of 80 yrs on this planet, I have two responses. 1) this IS how statistics work. They never poll everyone. They take a sample and base results on that. Always. This is constant. 2) The best prediction of future behavior is past behavior. We are creatures of habit and seldom change, especially in our ingrained habits – and predominately in those habits which we personally deem to be acceptable!
Fossil fuels poison the earth. From the way we extract them to the way we use them. Fossil fuels are limited. Whether or not we contribute to the change in weather patterns, these are facts. They warrant our attention and not to do so is again, just plain irresponsible.