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Global Warming

In this video Dr. Nathan B. English discusses global warming.
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Let's get stuck into the effects. We’ve talked about the causes of climate change, and sort of atmospheric greenhouse gases, and how they interact with solar radiation. And now I want to talk about the effects. And the effect we’ll talk about in this step is global warming. In the past, it was called global warming 20, 30 years ago. We’ve had an idea that this is an issue for over a century. Now it was realized that increasing CO2 from fossil fuel emissions would impact the climate.
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And then, in an early 2000s, people wanted to just, instead of saying global warming, we started to call it global climate change because we realized there were other things that were going to change as well, including rainfall and oceans. And now we can better parse out the impacts of global climate change. And in this step, we’ll talk about global warming.
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Now I want to revisit this little chestnut here, and I just want to remind you that incoming solar radiation is high frequency, a short wavelength, and it has lots of these atmospheric windows that it can travel through, where it hits the earth is absorbed by the surface of the earth. And then is re-emitted as long wave radiation with a low frequency. Okay, and then this is absorbed by the atmosphere, sort of based on the number of greenhouse gases, like carbon dioxide, methane,
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and other greenhouse gases. And then it’s re-emitted yet again as a long wave radiation,
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low-frequency radiation to either space, or back down towards earth. And it gets sort of trapped in this little cycle here. And the more greenhouse gases you have, the thicker, these two arrows become, and that where the heat content of your atmosphere, okay. So greenhouse gases add heat to the atmosphere through trapping heat, even though the incoming solar radiation is the same amount of energy as the outgoing infrared radiation, okay? So what comes in, goes out, it’s just how much of it is trapped in the atmosphere at any one time. Now note that the incoming solar radiation
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is about 340. That is about over 400 watts per meter squared. This graphic is in watts per meter square. And I say that because very small changes can have an impact on our atmosphere. So these are watts per meter squared at the top of the atmosphere, and watts per meter squared here at the surface of the atmosphere. And the changes we’re going to be talking about are in the one, four and eight watts per meter squared range. So very small changes, but they have a big impact.
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So this is a figure from the summary for policymakers of the IPCC report, the International Panel on Climate Change annual report, or sorry, Assessment Report six from page SPM-16. And basically this is the future anthropogenic emissions of key drivers of climate change and warming contributions by groups of drivers for the five illustrative scenarios used in this report. Now, I want to talk a little bit about the illustrative scenarios first, so you know what we’re looking at. Let’s take for example, panel A, which is carbon dioxide emissions in gigatons of carbon dioxide per year, okay? And there’s five lines on here, and I want to talk about what each line represents.
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Now, back here in 2015, we get to 2050, and then the year 2100, the next century here, okay? So time is on the x-axis and carbon dioxide emissions are on the y-axis. SSP stands for Shared Socioeconomic Pathway. I’m not going to talk too much about those, but you can look up Shared Socioeconomic Pathway, and look up what these are. These are sort of how our nations looking at climate change, and how are they interacting with the environment, and other nations around them. But at the end here is this 8.5, 7.0 is this number, okay? This decimal number. This decimal number refers to a representative concentration pathway. Now these were what they made scenarios out of in the previous report.
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And they’ve altered them just a little bit, but what the 8.5 and the 7.0, what the number represents is the watts per meter squared added to the earth surface based on a couple of scenarios. Okay, and these scenarios are basically how our nations decreasing, increasing, or maintaining their CO2 emissions, okay.
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SSP1-1.9. So this 1.9 scenario is if all countries had met their Paris Agreement targets, okay? This 2.6 scenarios, if we immediately adopt very stringent restrictions on CO2 and greenhouse gas emissions, okay? And that means at the, by the 2100 will have only added, anthropogenically added 2.6 watts per meter squared to the earth’s surface, okay? So that’s still an increase, right? That’s still an increase. Now I say that adding 2.6 watts per meter squared is about equivalent to a two degrees Celsius rise in temperature compared to that 1850 to 1900 time span. So that’s still a significant environmental impact.
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The scenario 4.5 is an intermediate scenario where we sort of begin to think about, at least begin to reduce our climate emissions. We have a 0% increase in carbon dioxide emissions by 2050. And after that, our CO2 emissions begin to decline as we begin to use less fossil fuels, and begin to use more alternative energy sources, and decrease our greenhouse gas emissions. So that’s sort of, that’s considered the intermediate scenario. And then 8.5 is where we forget about any kind of environmental restrictions on greenhouse gas emissions, and we go nuts. We burn all the fossil fuels, we’d just have a great time. This is like a big party. And then 2100 is the morning after.
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And we have to clean up. So 8.5 represents a scenario where greenhouse gas emissions from humans at 8.5 watts per meter squared to the surface of the earth. Now these also include some feedback effects as well, but that’s a really complicated, that’s for a whole nother course in climate science, but just want you guys have a relative idea of, these are different scenarios and where we end up with will be somewhere probably in between these. Now, I’ve also shown you the different scenarios for selected contributors to greenhouse gas, non-CO2 greenhouse gases, GHGs, so methane, nitrous oxide, and sulfur dioxide, okay?
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Now, as we reduce our dependence on fossil fuel emissions, we’ll also be reducing our sulfur dioxide emissions, which interestingly effect reducing silver dioxide emissions actually increases surface temperatures because they are an aerosol, light colored aerosol that reflect solar radiation rather than absorbing terrestrial radiation. Okay, so that’s where we’re sitting with these different scenarios. And I just want to make sure you understand what those different scenarios are, because now what we’re going to talk about is we’re going to talk about what those different scenarios mean for global surface temperatures. So these are the different scenarios impacts on average global surface temperatures
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in relation to 1850 to the 1900 average, okay? So this is how many degrees Celsius above the average temperature before 1900. Okay, and you can see that even the most optimistic scenarios where we drop everything we’re doing right now, switch to renewables and basically become carbon zero, and carbon capturing immediately. We’re still looking at a one to a 1.5, maybe 1.9 degree increase in temperatures
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between 2081 and 2100. So 50, 60 years from now, 60 to 80 years from now, okay. In scenario a 2.6, and remember, this is the very stringent scenario we’re looking at about a two degree temperature increase, scenario 4.5, almost a two and a half degree temperature increase. And in scenario seven and eight, we’re looking at between three and four and a half degrees Celsius increases in temperature compared to 1850 to 1900 average temperature.
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These would have a very large impact on global environments. Now, remember, these temperature changes are concentrated in the high latitudes. You’ll still get temperature changes in the tropics, but you might get a two degree, three degree temperature change in the tropics, and a six degree temperature change in the Arctic for an average temperature change of four, okay? But I’ll tell you what, a temperature change in the Arctic of six degrees Celsius is going to be real-real. You’re going to have a bad day because we’ll release a lot of methane, and there’s the chance that you get a positive feedback loop between temperature, and methane emissions.
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So this is sort of, this is the story for climate, and global temperature into the future. I think it’s important to think about what the causes are. And we spend a lot of time on the causes, but this is the effect.
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This is a table. This is Table SPM.1 again, from the same summary policymakers in the IPCC report. And it essentially looks at the near term changes in temperature. The midterm changes in temperature, so 20 to 40 years from now, and then the changes in temperature is 60 to 80 years from now. Okay, and they give you the very likely range, and this is, remember, these are based on models, and these models have probabilities. And the very likely probability I think is an 80% chance, right? And we all know that the race doesn’t always go to the swiftest nor the strongest, but that’s the way you bet.
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So there’s very likely range is where you put your money if you were betting at the race track. And in the near term, we’ll get roughly the same temperature increases for all the same scenarios. However, as we move into 2041 and 2081, the temperature differences between each scenario increased greatly. So you’ve got to about a temperature to two degree temperature difference 40 to 80 years from now between scenario 1.9 and scenario 8.5. Look, these are bad news.
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Yeah, I use bad news and I know that’s a value-laden judgment, but I don’t think there are very many environmental scientists who think increasing global temperatures by almost six degrees Celsius is going to have a positive impact. There’s lots of reasons to think it won’t, and lots of studies that show that it won’t. So we need to wrap our head around and very quickly begin to think of solutions to the causes of this effect, which is increased global warming over the next century.

So far we have focused mainly on the causes that contribute to global climate change. Now let’s turn our attention to the effects.

Watch Dr. Nathan B. English examine different scenarios and the increase in temperature that will result from each.

Video guide

Since this video is a little longer than most videos in this course, here is a guide to the topics it covers.

Topic Timestamp
Global warming 0:05
Revisiting radiation 1:15
Future annual CO2 emissions 3:10
What this means for global surface temperatures 8:10
Temperature increase scenarios 10:35

References

Figures SPM.1, SPM.2, SPM.5 and SPM.8 from IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson- Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.
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