Home » Climate Change » Global Warming of 1.5°C (2)

Global Warming of 1.5°C (2)


In the previous post, I reported that the recent IPCC report, Global Warming of 1.5°C, concludes that it is theoretically possible to limit global warming to 1.5°C, but it would require drastic change: a 50% reduction in GHG emissions by 2030, and zero net GHG emissions by 2050. In this post, I will discuss some of what the report says about making such a change.

The IPCC reviewed a number of computer models to explore scenarios that limited global warming to 1.5°C. Assumptions varied between the models, and they consequently yielded different results. They can be grouped into several categories: models that projected an increase in Global Mean Surface Temperature (GMST) that stayed below 1.5°C, models that projected a small overshoot of 1.5°C (eventually returning to 1.5°C), models that projected a large overshoot of 1.5°C (eventually returning to 1.5°C), models that projected a 2.0°C increase in GMST, and models that projected a large increase above 2.0°C.

CO2 Emission Price

Figure 1. Source: Intergovernmental Panel on Climate Change, 2018.

According to the report, limiting the increase in GMST to 1.5°F would require putting a substantial price on carbon emissions. Estimates vary widely, thus, there is substantial uncertainty about just how large the price increase would need to be. It is clear, however, that the smaller the increase in GMST, the higher the price would have to be, and in all cases, the price would need to rise over time. Figure 1 shows the findings. The required price of carbon emissions is on the vertical axis, and the year is on the horizontal axis. The different colored columns represent the categories defined in the preceding paragraph.

The projected price for 2030 ranges from $135 to $5500 per metric ton of CO2e. The projected price in 2050 ranges from $245 to $13,000 per metric ton of CO2e. For comparison, at 11:22 a.m. CST on 12/4/18, Bloomberg reported the current price for emissions on the European Emissions Exchange was €20.72 ($23.48). Thus, the estimate for 2030 ranges from about 6 to 234 times the current price. I don’t know if fossil fuel prices would increase equally, but you can be sure they would increase a lot!

Carbon pricing, however, would not be sufficient in and of itself, and other policies would be required. The strategies mentioned in the report include using less energy, converting electricity generation to methods that don’t release carbon dioxide, converting all fuels to types that don’t release carbon dioxide, converting all energy end use to use decarbonized electricity (e.g. electric cars that run on renewable electricity), and some form of carbon sequestration. This is an intimidating list of changes. It would involve transforming basically all of our energy use infrastructure.

I couldn’t find an estimate of the cost of making the required transformation.

Threats to systems

Figure 2. Source: Intergovernmental Panel on Climate Change, 2018.

IPCC also doesn’t make specific predictions about the consequences of unchecked global warming, such as “Miami will flood,” or “400 million people will die of famine.” Rather, they speak of threats, how many people will be exposed to them, and which natural systems will be impacted. Figure 2 shows that for all of the systems considered, the threat increases the higher GMST goes. The increase in GMST is shown on the vertical axis. In the columns, white means the system will not impacted. Yellow means it will be impacted moderately. Red indicates that the impact will be severe and widespread. Purple indicates that the impacts will not only be severe, but perhaps irreversible, and also that the ability to cope with and adapt to the change will be limited. It is easy to see that for all systems, the risks increase as global warming increases. Some of the systems enter the red or purple color at or below 1.5C. But many of them only turn red or purple between 1.5 and 2.0°C.

The consequences are dramatic. The report discusses the specifics at great length, and they are far too numerous and complex to try to summarize here. However, I will say that the reports quotes estimates that, if no policy is instituted to limit global warming, GMST would rise 3.66°F by 2100, and it would reduce global Gross World Product (GWP) by 2.6%. According to the CIA World Factbook, GWP in 2017 was $127.8 trillion. Thus, even if GWP does not grow over time, a 2.6% reduction would equate to $3.3 trillion. In comparison, limiting global warming to 2°C would result in a decrease in GWP of 0.5% ($639 billion), and the 1.5°C scenario would result in a reduction of 0.3% ($383 billion).

Thus, the damage associated with global warming increases dramatically the more it warms. Limiting climate change to 1.5°C compared to 2.0°C would prevent $256 billion in economic loss every year. Thus, over a 10-year period, if you spent $2.5 trillion on climate change prevention, it would still be justifiable on the basis of avoided damage. A few trillion dollars here, hundreds of billions of dollars there – pretty soon, it will add up to real money!

The report includes population projections in its modeling of future climate change: increasing the population increases GHG emissions, and hence, it increases future climate change. The report does NOT address, however, limiting population as a strategy for limiting climate change, and least I could not find a section that did. Hmm! (If it’s there and I missed it, please let me know in a comment.)

The report is based on more than 6,000 scientific references. It contains a great deal of information, far too much to adequately summarize here. It should make clear, however, that the denial of climate change is no longer viable. If you ask me, it’s been clear for a long time, but this is pretty definitive.

Drastic change is required immediately if we are to avoid terrible damage to our planet. Even in only economic terms, the projected damage if we do nothing is absolutely staggering. Can humankind respond with the kind of immediate, large-scale planetary change that is required, or is it already too late?


Bloomberg.com. Markets: Energy. Viewed online 12/4/2018 at https://www.bloomberg.com/energ.

Central Intelligence Agency. 2018. The World Factbook 2016-17. Viewed online 11/30/2018 at https://www.cia.gov/library/publications/the-world-factbook/index.html.

Intergovernmental Panel on Climate Change. 2018. Global Warming of 1.5°C (Draft). Downloaded 11/24/2018 from https://www.ipcc.ch/report/sr15.

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