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How Do We Know That Humans Are Causing Climate Change? These Nine Lines of Evidence


While most Americans acknowledge that climate change is happening, some are still unsure about the causes.

They are often labeled “climate skeptics,” but that label can cause confusion or even anger.

Isn’t the nature of science to be skeptical? Isn’t it good to question everything?

Yes, but —

Here’s what is getting lost in the conversation:

Scientists have been asking these questions for nearly 200 years. The scientific community has been studying these questions for so long that collectively they have amassed an overwhelming amount of evidence pointing to a clear conclusion.

A similar situation is smoking and cancer. Nowadays, no one questions the link between smoking and cancer, because the science was settled in the 1960s after more than 50 years of research. The questions have been asked and answered with indisputable evidence.

We can think of the state of human activities and climate change as no different than smoking and cancer. In fact, we are statistically more confident that humans cause climate change than that smoking causes cancer.

Our confidence comes from the culmination of over a century of research by tens of thousands of scientists at hundreds of institutions in more than a hundred nations.

So what is the evidence?

The research falls into nine independently-studied but physically-related lines of evidence, that build to the overall clear conclusion that humans are the main cause of climate change:

  1. Simple chemistry that when we burn carbon-based materials, carbon dioxide (CO2) is emitted (research beginning in 1900s)
  2. Basic accounting of what we burn, and therefore how much CO2 we emit (data collection beginning in 1970s)
  3. Measuring CO2 in the atmosphere to find that it is indeed increasing (measurements beginning in 1950s)
  4. Chemical analysis of the atmospheric CO2 that reveals the increase is coming from burning fossil fuels (research beginning in 1950s)
  5. Basic physics that shows us that CO2 absorbs heat (research beginning in 1820s)
  6. Monitoring climate conditions to find that recent warming of the Earth is correlated to and follows rising CO2 emissions (research beginning in 1930s)
  7. Ruling out natural factors that can influence climate like the Sun and ocean cycles (research beginning in 1830s)
  8. Employing computer models to run experiments of natural vs. human-influenced “simulated Earths” (research beginning in 1960s)
  9. Consensus among scientists that consider all previous lines of evidence and make their own conclusions (polling beginning in 1990s)

(You can also see these nine lines of evidence illustrated in the graphic below)

Skeptics sometimes point to the last two supporting lines of evidence as weaknesses. They’re not. But even if you choose to doubt them, it is really the first seven that, combined, point to human activities as the only explanation of rising global temperatures since the Industrial Revolution, and the subsequent climate changes (such as ice melt and sea level rise) that have occurred due to this global warming.

The science is settled, and the sooner we accept this, the sooner we can work together towards addressing the problems caused by climate change – and towards a better future for us all.

By Ilissa Ocko


24 Comments on "How Do We Know That Humans Are Causing Climate Change? These Nine Lines of Evidence"

  1. coffeeguyzz on Mon, 27th Mar 2017 9:29 pm 

    … Naaahh

  2. Go Speed Racer on Mon, 27th Mar 2017 10:12 pm 

    There is no climate change, and if there
    were, then it’s occurring naturally.

    I know this because of yesterday’s
    sermon from the pastor. He spoke for
    almost 10 minutes this very issue.

    Then we sang, and then was the collection
    plates. I put in an extra $20 for his Godly
    explanation that humans cannot affect the
    Earth’s climate. And that’s what Trump said too.

  3. Plantagenet on Mon, 27th Mar 2017 10:38 pm 

    Is it possible to send a tweet about this to President Trump?


  4. GregT on Mon, 27th Mar 2017 10:42 pm 


    I’m sure that a twit like you could figure out a way to tweet Trump.


  5. Midnight Oil on Mon, 27th Mar 2017 10:46 pm 

    But the real question what is the break even point of Tar Sands?

  6. forbin on Tue, 28th Mar 2017 2:34 am 

    oh its the methane , not the CO2, but I know you can check this yourselves on posted data on the internet ( as many have ) .

    not sure we’re expecting the results though ….


  7. Go Speed Racer on Tue, 28th Mar 2017 3:31 am 

    Methane is the problem,
    So everybody stop farting.

  8. Cloggie on Tue, 28th Mar 2017 4:56 am 

    As the article states, nobody denies the thermometer readings or the size of the arctic ice sheet.

    Under dispute is:

    – how bad is it?
    – How bad is it going to be?
    – Is CO2 the cause and/or the only cause?

    It is now end of March. Yesterday my modest 6 solar panels generated a record 8.2 kWh, that is double my average yearly consumption and it is only end March.

    The weather… the Germans have a name for this kind of weather:


    (Emperor weather).

    Deep blue skies, strong sun. And although the air temperature yesterday was “only” 15 Celsius , the radiation gives a feeling of early Summer. Yesterday my neighbor was eating on the garden terrace with his shirt off to work on his skin tan.

    It will be a record low this year as far as fuel costs are concerned. There was no snow and perhaps a few days of ice allowing for some skating.

    As far as Holland is concerned… if this is the new weather, I’m all for it.

  9. onlooker on Tue, 28th Mar 2017 5:20 am 

    Clog, you remind me of the oft used frog in boiling water analogy. Wow

  10. Davy on Tue, 28th Mar 2017 6:08 am 

    Too bad 97% of these climate scientist and their liberal leaning supporters don’t acknowledge what many of the other predicaments mean. They believe there are techno solutions to the climate predicament. They think the global economy is going to keep printing out their paychecks. Few of them want to say we need to reduce population to bellow 1BIL. Few of them believe in turning away from affluence and complexity because that is what science has become. None of them want to do this because we live in a weird world of blame and complain. We live in a world where only optimism sells. We live in a strange world of specialization and tunnel vision. Many of these climate scientist are just as delusional as a DJT supporter science denier clowns just at a higher level of smarts. When the really smart are delusional you got a fiasco on your hands. When you have scientist in denial then the game is over. It is over anyway so what the hell let them live with some hope. Hope keeps civilization humming.

  11. Nony on Tue, 28th Mar 2017 8:21 am 

    The key issues are really 6, 7, and 8. No one doubts that CO2 has risen. But the question is attribution of the temperature rise (and prediction of rise still in the pipeline). Much of that list is like saying metal is hard, therefore someone knifed their wife.

    The problem is that the amount of temperature rise is dependant on a large amount of water vapor feedback. CO2 on its own absorbing directional IR and then scattering it spherically can only explain a small fraction of the temp rise. How water vapor feedback works is not really clear since we are talking about a dynamic system with transport and all that.

    You may hear some hand waving about Clausius Clapeyron, but open your Atkins p chem book and look at the equation. The system assumptions are not met. Nor is the equation really even used. It is just making the qualitative argument (that some extra water vapor is boiled off and gives more effect for the CO2–H2O is a powerful greenhouse gas). No one actually uses the C-C equation to calculate extents of warming. The system is dynamic. People use computer models to try to calculate the added H2O effect. It is just using a fancy word.

    This is not to say that I am anti global warming “consensus”, but just that it is not clear to me. Could see the effect being 50% worse than the modelers think or 50% less bad. There are a lot of knobs to turn in those models. You guys complain about EUR models. But a climate change model has even more parameters to adjust.

    P.s. I have a Ph.D. in a hard science and have worked in several different technical fields. I am not blown away by someone having the “union card”. Much of the “consensus” gets fuzzy if you really look into who has deep knowledge of the key evidence (computer models) and who is just an educated bystander like anyone else.

  12. Apneaman on Tue, 28th Mar 2017 11:40 am 

    Trump says -Get use to being ignored when the next AGW jacked event hits you and yours.

    In wildfire’s wake, the president’s silence is deafening

    “We in rural America don’t ask for much. But sometimes, that’s exactly what we get.

    Farmers and ranchers are resilient. They have to be, when they’ve spent generation after generation weathering storms, drought, low prices and now…wildfires.

    The trouble is, now they need help. And President Donald Trump’s administration has not yet responded.”

    “Yet, we’ve heard nothing from the Oval Office. Not a word about the disaster, not a peep about assistance. The most noteworthy news item coming from the Oval Office the last few weeks (aside from a meeting the president had with Germany’s Chancellor, Angela Merkel) is that of the feud President Trump has with a rap star named “Snoop Dogg.”

    Most of the people in this retard state are deniers and voted for that fat orange fuck, so suffer bitches.

  13. Apneaman on Tue, 28th Mar 2017 11:53 am 

    Heatwave in Odisha: Mercury Level Reaches 43 Degree Celsius in Titlagarh

    Heatwave across Gujarat, city sizzles at 42.8°C

  14. Apneaman on Tue, 28th Mar 2017 12:09 pm 

    “The science is settled,…”

    No it’s not. What all the evidence points to is that it’s happening (no science needed for that) and the humans have triggered it. That’s what almost all the evidence indicates. Science is never “settled”. Anyone can present new evidence and data that brings into serious doubt or overturns an accepted finding at any time for AGW, evolution, gravity or any other scientific theory. Falsifiable. Anyone who actually understands what science is should know this. Scientists are some of the most curious and competitive people on the planet and will argue over minutia all damn day, so in that regard things are never settled and especially when most new discoveries garner even more mysteries and questions. Almost no one is arguing that humans are the trigger this time, but they are arguing about many other things. One thing most of them got wrong was the timelines.

    “Faster than previously expected” is the order of the day.

    Faster Than Expected

    The world, she is a-changing, faster than expected

    Prep, pray, party……..the end is neigh kids.

  15. GregT on Tue, 28th Mar 2017 12:21 pm 


    “The key issues are really 6, 7, and 8.”

    For you perhaps. Ignoring 1, 2, 3, 4, 5, and 9, points to denial. #8, “because we can’t experiment with the earth”, is kind of silly, because that is exactly what we are doing.

  16. Apneaman on Tue, 28th Mar 2017 12:24 pm 

    Study: “Global warming triggered by the massive release of carbon dioxide may be catastrophic, but the release of methane from hydrate may be apocalyptic.”

    “Oldspeak: “The study, titled “Methane Hydrate: Killer Cause of Earth’s Greatest Mass Extinction,” highlights the fact that the most significant variable in the Permian Mass Extinction event, which occurred 250 million years ago and annihilated 90 percent of all the species on the planet, was methane hydrate.

    In the wake of that mass extinction event, less than 5 percent of the animal species in the seas lived, and less than one-third of the large land animal species made it. Nearly all the trees died….

    The scenario that humans have created by way of the industrial growth society is already mimicking these eventualities, which are certain to worsen….

    As the global CO2 concentration continues to climb each year, the threat of even more abrupt methane additions continues to escalate along with it….”

  17. rockman on Tue, 28th Mar 2017 2:37 pm 

    The Rockman continues to be amazed by those who think proving AGW is the key to changing the path the world is on. Same situation with the folks who deny the possibility of AGW.

    Both sides of the debate are wasting their energy IMHO. The fossil fuel consumption dynamic is not changing by any meaningful amount. And no consensus about AGW will change the situation. The world’s population demands energy. And it demands it at the lowest possible cost. Unless someone can change that atitude it doesn’t matter if ever soul on the planet accepts AGW. It will just be the price willingly paid by mankind for what it wants.

    The truth is readily apparent: look at the countries where the politicians and public express the greatest concern over climate change. Now list the SIGNIFICANT changes being accepted by the voters. And add how much meaningful reductions those voters have accepted of their lifestyles.

    And to be clear: significant ACTIONS…not words. And for those believing in AGW: OK, how do you propose getting the global fossil fuel consumers to change their ways? And convincing them AGW exists is not one of your methods for the simple reason that efforts to do so have met no significant results as proven by the fact that the world is current consuming fossil fuels near the highest level in history.

  18. You Don't Want to Know Me on Tue, 28th Mar 2017 2:39 pm 

    “97% of these climate scientist and their liberal leaning supporters”

    Yes, the climate is a left right issue. That’s’ right.

    Capitalism, the way it works, demands that there be a ‘left’ and a ‘right’ with the left being the people who work and the right being the owners of capital.

    People who continue to regard the world through that old tired lens are pretty dense. No hope in talking to those block heads – their minds are caught in the clay of old thinking.

    Capitalism works great when there are surplus resources that are easily and cheaply extracted, manufactured into consumer products and then resold at a profit.

    Easily and cheaply extracted resources being the key here. Those are going away.

  19. onlooker on Tue, 28th Mar 2017 2:46 pm 

    Right you are You about Capitalism and the Left-Right spectrum

  20. You Don't Want to Know Me on Tue, 28th Mar 2017 3:30 pm 

    “OK, how do you propose getting the global fossil fuel consumers to change their ways? ”

    I don’t because they won’t.

    While I accept the science of AGW I don’t believe for a second that we, homo sapiens sapiens, will ever do a goddamn thing about it. For the very reasons you mention.

    Well said rockman.

  21. Apneaman on Tue, 28th Mar 2017 5:27 pm 

    rockman, you’re still stuck in your monkey tribe mentality where you think everyone who “believes” in AGW (convinced by the overwhelming evidence and real time destruction actually) is advocating for the humans to change. Not paying attention to the growing number of humans who see that it is far too late now and definitely not reading the wealth of links I have provided containing mountains of evidence that demonstrates that the humans are no more in control of their behaviour than a shark or an oak tree.

    So lets say X amount of people are convinced that it’s game over for civilisation and probably the species what percent of them do you estimate would publicly say so? How many scientists, politicians, bureaucrats or famous people would actually come out and say it if they were convinced that was the human’s fate? How about none of them if they wish to remain employed and keep their social standing.

    Now the retired guys are a different matter. Can’t fire them and there is also that phenomena where many older people are tired of a lifetime of the bullshit and stop caring what the other monkey’s think.

    Humans will be extinct in 100 years says eminent scientist

    “( — Eminent Australian scientist Professor Frank Fenner, who helped to wipe out smallpox, predicts humans will probably be extinct within 100 years, because of overpopulation, environmental destruction and climate change.

    Fenner, who is emeritus professor of microbiology at the Australian National University (ANU) in Canberra, said homo sapiens will not be able to survive the population explosion and “unbridled consumption,” and will become extinct, perhaps within a century, along with many other species.”

    Read more at:

    “Wildlife biologist Neil Dawe says he wouldn’t be surprised if the generation after him witnesses the extinction of humanity.”

    Kinda hard to play that old “grant money” card on retired guys who say it’s too late eh? I remember petroleum geologist Colin Campbell admitting on camera in one of the peak oil documentaries that he lied like a dog when he worked for Shell – of course he did.

    Then there are the many scientists who have been saying for a number of years that the humans could/will go extinct if they don’t change. Not changing – can’t really.

    Humans could be among the victims of sixth ‘mass extinction’, scientists warn

    “”If it is allowed to continue, life would take many millions of years to recover and our species itself would likely disappear early on,” lead author Gerardo Ceballos of the Universidad Autonoma de Mexico said.”

    rockman you just keep up the bad work with your oily apologetic because we don’t want you to feel to bad about all the lying you do to protect your social status and conscious. Like the heroin dealer you are just giving the humans what they want right? This is good. This way you don’t need to feel bad about all the lying, denial and deceiving. Just because it’s a deterministic universe and the humans can’t help themselves does not give you and your oily scum fuck friends a free pass. Y’all have broken more laws and operated under more bad faith as any group of greedy cock suckers in human history. I tend to think you know this given your never ending apologetics for what you do. Otherwise why so vigorously defend? No righteous man could possibly be as defensive and touchy as you are.

  22. Apneaman on Tue, 28th Mar 2017 5:32 pm 

    Record Low Sea Ice Maximum a Lock as Arctic Continues Trend of Ridiculous Warmth

    “Temperatures in these warm air invasion zones are expected to rise to between 10 and 30 degrees Celsius above average (18 to 54 F above average). In some places covering these warm wind invasion zones, we are also expected to see sporadic above freezing readings and, in the case of the Laptev — periods of liquid precipitation over the sea ice”

    Frailest-Ever Winter Sea Ice Facing a Cruel, Cruel Summer

  23. Apneaman on Tue, 28th Mar 2017 5:38 pm 

    Communities Retreat as Oceans Swell, Coasts Erode

    “Erosion, rising seas, ferocious storms and other coastal perils have prompted the resettlement of more than 1 million people worldwide, with an exhaustive new analysis highlighting an emerging migration crisis that’s worsening as global warming overwhelms shorelines.

    Researchers scoured journal papers, government reports and news articles for examples of what experts call “managed retreat,” analyzing 27 rules, programs and decisions that have led to the abandonment of homes and homelands from Louisiana, New York and Alaska to Thailand, Brazil and Australia.”

  24. GregT on Tue, 28th Mar 2017 9:42 pm 

    “While I accept the science of AGW I don’t believe for a second that we, homo sapiens sapiens, will ever do a goddamn thing about it. For the very reasons you mention.
    Well said rockman.”

    Completely agree. The consequences of ending greenhouse gas emissions would be immediate, and horrific. The horrific consequences of doing nothing, will be our legacy to our children.

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