How do we know humans are causing climate change?

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It pains me to have to write a blog on this topic in 2019. I feel that at this point, people who claim they haven’t seen enough evidence that humans are changing the climate are, frankly, just not looking very hard. Plenty of people have covered this topic in the past and there are some great summaries available, at all different levels of scientific detail.

Nevertheless, this is a question I’ve found myself being asked to address repeatedly over the last few weeks and months. So I thought I would just write down my answer here instead.


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Annual global temperatures from 1850-2017. Image used under a creative commons license from Climate Lab Book.

2 comments on “How do we know humans are causing climate change?

  1. With all this evidence, one would think you would be able correctly say what the future looks like. Sadly, none have been right. I got a question though. How are we going to run out of fossil fuels if the earth naturally makes them? Oil is made through bacteria. Coal comes from plant decay. We were told in the 1970s that we had reached “Peak oil.” I remember the bumper stickers. Back then it was called Global Cooling. Then it was switched to Global Warming. Both are one narrative each, but Climate Change. Well, you have an infinite amount of narratives. Also, if this is do real why have you been caught in lies? Why did NOAA fabricate data to make it appear the earth was warming faster than it was? Why when a group of scientists took a ship to Antarctica to prove the ice was melting and when they got stuck, why did the media ignore it and the ones that did cover it call it a cruise ship? Why are the biggest pushers for this the worst polluters? Why is this a problem that the government can only save? Why do you use Antarctica as places for testing? No one lives there. No one is able to fact check your claims? How is a world that is covered by .03% of people able to change the environment? Why did Obama’s Clean Air Act end up leaving taxpayers on the hook for 3 billion dollars? One would think it would have the opposite effect if it’s such a good thing. All your claims say well, it hasn’t been like this for this many years. So, what you’re saying is we did have levels like this before when their was no coal plants? Otherwise you would if said there has never been anything like this ever. Why is it that the solution is to give the government all our money? If you only care about the environment, why is the government pushing things like “Climate Change Racism?”

    • Hi Matt,
      Thanks for taking the time to read my post!

      Let me address your points one by one:
      The reason we are running out of fossil fuels even though they are naturally produced is that fossil fuels take an extraordinarily long time to produce. It takes millennia of high temperatures and pressures to turn the remains of living organisms into crude oil, natural gas or coal. People have been warning that we are running out of fossil fuels for some time, that is true, however part of the reason that ‘peak oil’ keeps moving is that as oil prices go up, reserves that were previously not financially viable to extract have become profitable. Also, as climate change has begun to melt ice sheets, previously inaccessible reserves have come into play. However, this cannot go on forever and we will eventually run out.

      Before it became clear that greenhouse gases in the atmosphere were accumulating and the Earth was warming, some scientists warned of global cooling because, based on natural cycles of temperature, we should be heading into an ice age sometime soon. The fact that we aren’t, and instead we are experiencing accelerating warming, is evidence that humans have disrupted the natural, long-term cycles of global temperature that have existed for millenia.

      As I said in my post, there have been times in Earth’s history when it has been this warm, and when greenhouse gases in the atmosphere have been this high, but it has been millions of years since those conditions last occurred. In some cases, scientists make the statement that conditions like this haven’t been seen in at least X number of years – in these cases it may simply be that that is when our records go back to! Furthermore, on those occasions when conditions have changed this rapidly, mass extinctions have occurred. I’m not saying the Earth can’t survive the climate change humans are causing, but it’s quite possible that most life on Earth cannot – humans included.
      I don’t know what evidence you are referring to that NOAA fabricated data, that is quite an allegation – please can you share your sources?

      I’m afraid I don’t know what you mean about the ship in Antartica, or the suggestion that those who pollute the most are advocating for climate change more strongly. Again, could you please elaborate / share your sources?

      I don’t believe that governments will be the only players in addressing the climate emergency, but they have an important part to play. History has shown that without adequate regulation, some companies will always put profit over environmental sustainability. At present, many governments worldwide have policies that actively incentivise continued fossil fuel use even when renewable technologies have become cheaper.

      Antartica is an excellent place for gathering scientific data for many reasons – it holds an extensive record of past climate in the ice, it is a temperature-sensitive ecosystem that can act as an early warning about significant changes in global climate, and it is, in many ways, relatively untouched by humans. However, evidence for climate change has and is being collected worldwide – in temperate regions and tropical, in forests and savannahs, on islands and deep within continents.

      I don’t find the argument that there are two few humans to affect climate convincing at all, there are over 7 billion of us and we inhabit every continent of the globe. As I discussed in my blog, “How much land on Earth is inhabited”, humans have impacted the vast majority of the world. Not to mention that we have compelling evidence from multiple independent sources that the climate is changing as a result of human activities.

      I can’t comment specifically on US politics, but sometimes technology that will result in a vast improvement in the long term requires a short-term investment.

      As I said in my post, there have been times in Earth’s history when it has been this warm, and when greenhouse gases in the atmosphere have been this high, but it has been millions of years since those conditions last occurred. In some cases, scientists make the statement that conditions like this haven’t been seen in at least X number of years – in these cases it may simply be that that is when our records go back to! Furthermore, on those occasions when conditions have changed this rapidly, mass extinctions have occurred. I’m not saying the Earth can’t survive the climate change humans are causing, but it’s quite possible that most life on Earth cannot – humans included.

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