Lecture 16 Predictions Of Future Climate And Its Effects PDF

**Lecture 16 Predictions** **of future climate and its effects** Prediction of climate is not an easy task, in part because it is difficult to measure the many factors involved (value uncertainty) and in part because there are many possible ways these factors can interact (structural uncertainty)....

**Lecture 16 Predictions** **of future climate and its effects** Prediction of climate is not an easy task, in part because it is difficult to measure the many factors involved (value uncertainty) and in part because there are many possible ways these factors can interact (structural uncertainty). We are not only unsure of how climate will change in the face of increasing CO~2~, but also how much more CO~2~ will be released. Rather than attach uncertainty to CO~2~ release, in its 5^th^ report the Intergovernmental Panel on Climate Change (IPCC) considered four different scenarios (Fig. 1). Annual emissions are presently lower than the most extreme scenario, but higher than the others. While emissions have recently decreased in the USA and Europe, they are increasing in India and elsewhere, with the result that 2023 recorded the highest emissions up to that point (Fig. 2). **Figure 1** Four scenarios for how emissions of CO~2~ (tonnes of carbon) due to fossil fuel burning may change over this century, as used by the Intergovernmental Panel on Climate Change in modelling climate at the end of the last century. Actual emissions are in orange. The scenarios are based on assumptions about social pressures, technology, population, etc. The high emissions scenario is now considered extremely unlikely, as it required large increase in coal use. The lowest emission curve becomes negative as a result of carbon capture techniques. Temperature increases at the end of the century are the 0.5 probability predictions (i.e., there is a 50% chance of this temperature being reached, given the model assumptions). **Figure 2** Annual emissions due to fossil fuels and cement production. The total CO~2~ released by humans correlates with the maximum temperature that will be reached in the future. The IPCC estimates that 1 trillion tonnes (a million million tonnes) of carbon released gives about a 1 in 3 chance of a 2^o^C average global temperature raise. Three of the four scenarios in Figure 1 predict we will pass this point around about 2050. The most extreme emissions scenario considered by the IPCC, would with 0.5 probability, give a 4.5^o^C rise or more by 2100. While we are not on course for this rise, even the other, less dramatic scenarios lead to rises of at least 3^o^C, 2.5^o^C, 1.8^o^C, respectively, with 0.5 probability by the end of the century (Fig. 1). The other leads to the lowest outputs; it assumes not only cuts, but carbon capture. Given these scenarios, the rest of this lecture: \(1) Summarizes expected consequences of climate change. \(2) Evaluates ways to slow and reverse emissions, emphasizing the importance of renewables. **Consequences of climate change: one, two and three degrees** *One degree:* A 1^o^C rise is about as warm as it has been over last 10,000 years and is similar to estimated average temperatures for the last inter- glacial, which were associated with sea levels 6 m--11m higher than now. The temperature across the world in 2024 was already 1.5^o^C warmer. If it would be possible to completely stop releasing fossil fuels tomorrow, CO~2~ should decline to 350 ppm by 2100, being absorbed by the oceans, and temperatures at the end of the century might be like today. Alternatively, annual 5% cuts are expected to lead to a temperature increase to mid-century, followed by a slower decline. *Two degrees* 2^o^C is problematic for several reasons. First, a 1^o^C rise has caused extreme events already, as we noted with respect to heat waves in the previous lecture, and probably applies also to storms and hurricanes. While it will get wetter globally by a few percent, we expect redistribution of rainfall to create droughts in some places and floods in others (Fig. 3). It takes some time for sea level rise to happen, but under all four emissions scenarios, the end of the century prediction is that of a further 0.3m increase in sea level with a probability of 0.95. Even if we stopped all emissions tomorrow, a greater than 1.5m rise is expected over the next 2,000 years. Third, ongoing disruptions of populations as they respond to the changing climate will bring undesirable side-effects, such as an increase in the geographical A map of the world Description automatically generated**Figure 3** Predicted changes in precipitation by mid-century, with respect to the period 1986 to 2005. Changes are modelled based on the 3^o^C scenario of Figure 1. In this case, wet, wetter and very much wetter are annual increases of \40cm a year. In most locations experiencing a decrease, the decrease would be less than 5 cm/year, but these are often relatively dry already. scope of malaria. Fourth, all sorts of positive feedbacks are possible over the longer term, especially as CO~2~ levels are much higher than they were during the previous interglacial periods. The impact of feedbacks is difficult to assess. A very big question is whether the terrestrial environment will turn from an absorber of carbon to an emitter of carbon, as the northern regions warm up and permafrost melts. With a 2^o^C rise, feedbacks may take us on the route to 3^o^C. *Three degrees* A 3^o^C or greater warming is seen to be disastrous, even without considering feedbacks. At 3^o^C, Mark Lynas writes about the Amazon rainforest: *"A new unrecognizable landscape is born. In the deepest parts of the basin, where once the only sound was the howling of monkeys and the rustling of leaves, a moaning wind has arisen. Dust gathers in the lee of burned out tree stumps. Nearer to the ground, a gentle hissing sound is heard. Sand dunes are rising. The desert has come."* This seems realistic, given the recent droughts in the Amazon described in the previous lecture, predictions of how precipitation patterns will change, which include a drying out of the Amazon, and the confounding effects of deforestation, which itself reduces local precipitation. **Limiting CO~2~ build-up** Various conservation measures could possibly reduce CO~2~ emissions. For example, we could reduce the number of kilometers driven by cars and increase use of public transport, or the automobile industry could increase car efficiency (kilometers per gallon). A problem with increased efficiency, however, is that the associated price reductions often generate increased **Table 1**. Emissions of CO~2~ for the manufacture of gasoline from oil, or of ethanol from corn \* ----------------------------------------------------------------------------------------- -------------- ----------------------- **Gasoline** **Ethanol from corn** **Extracting/Growing** 1 7 **Refining** 4 11 **Burning for energy** 20 19 **Recovered when growing** 0 -17 **Total** **25** **20** \*grams of carbon per megajoule energy. consumption, and these may surpass the original efficiency savings, at least in a world where people are getting generally wealthier (Jevons\' paradox). Alternative routes to reduce emissions despite ongoing consumption include capturing carbon during the generation of energy from coal or biofuel, using cleaner sources of energy on a massive scale, including solar, wind, hydroelectric, nuclear, or even natural gas (which is cleaner than coal), increasing forest cover, and relying more heavily on biofuels. Any switch to sources of energy that release less CO~2~ should help. All such sources have some undesirable side-effects, from dams limiting water flows and destroying forests, to nuclear waste, to bats and birds flying into wind turbines and the land needed for such turbines, although none appear to be as serious in the long term as continuing to fossil fuels. Below, we consider some of these options in more detail. Overall, the importance of turning to renewable sources becomes clear. *Biofuels* Biofuels are plants used for fuel rather than food. At present, crops such as corn and sugarcane are the main biofuels. In theory, all the carbon released when the crop is burned for energy is recaptured when the same crop is grown the following year, hence it is "carbon neutral." In practice, however, no biofuel can possibly be carbon neutral because it takes energy to grow, harvest and refine the crop. Table 1 shows some calculations for corn grown as a source of ethanol in the US. This table shows that when emissions associated with growing, harvesting and refining are accounted for, net CO~2~ emissions from biofuel are only about 20% less than from oil. The reason is that growing and refining the biofuel emits more than three time the quantity of CO~2~ than is emitted when extracting and refining oil. Nevertheless, on the face of it, this is a **Figure 4** Carbon released as a result of conversion of natural land to that growing biofuels, and time to repay the generally small gain in CO~2~ savings, which depends on the type of biofuel (in grey). Estimates are based on carbon released over 50 years, but especially Indonesian peatlands are expected to release carbon beyond that time horizon. saving, albeit a relatively small one. Some biofuels are quite efficient, and sugarcane gives about an 85% reduction in CO~2~ emissions because it can be refined more easily than other crops. There is, however, a problem with this accounting. Biofuels as used today are made from crops that take up land, which could be used for something else. Further, if wildland is converted to biofuel, the cost of land conversion in terms of emissions can be large. Vegetation is burnt and rots and even harvested timber eventually decays, releasing CO~2~. Converting midwestern grassland to corn releases sufficient CO~2~ into the atmosphere that it would take more than 90 years for the 20% savings in CO~2~ to compensate (Fig. 4). When tropical forest on peat (compressed vegetation) is converted to palm oil plantations in Indonesia (e.g., around Gunung Palung National Park in Indonesia), the small savings in CO~2~ from their use as biofuel takes several hundreds of years to compensate for the CO~2~ released (Fig. 4). One reason is that the peat continues to emit CO~2~ for many years as it dries out. Given that we are concerned about CO~2~ release in the next decades, the use of these kinds of biofuels is making things worse not better. Growing crops for biofuels places pressures on the world's food supplies and natural habitats. Moreover, with current methods, crops grown on land can provide only a small proportion of all energy requirements. In 2019, 40% of corn grain in the US was used for biofuels, implying about 12% of all agricultural land in the US was used to provide corn grain for biofuel, a number that has held steady for 10 years, but which provides only 7% of total liquid fuel consumed in the US. New biofuels, e.g., algae cultured in tanks, may be more successful. *Fracking* Fracking "hydraulic fracturing" has rapidly increased over the past 20 years resulting from technological improvements, and now accounts for about 80% of all gas extracted in the US. Water and chemicals, many of which are themselves pollutants, are forced underground under pressure to eject the gas (classically this has contaminated water supplies, and in one case, one could turn the tap on, and light the fluid emerging). In 2005, the US Congress passed a provision in the Energy Policy Act that exempted gas companies from the Clean Air and Clean Water Acts, thereby stimulating a great surge in natural gas exploration. In 2010 in the USA gas contributed about half as much electricity to the grid as coal, but gas now contributes more than twice as much electricity as coal; is a four-fold increase in the relative contribution of gas. For the same energy production, CO~2~ emissions from gas are about one-half those from coal, and this is one reason why CO~2~ emissions have declined in the USA (increases in efficiency and in renewables also contribute). However, gas largely consists of methane, some of which escapes into the atmosphere. Over the last 20 years methane has increased at a steady rate in the atmosphere. Molecule for molecule methane traps heat \~120x more effectively than CO~2~ and is considered responsible for 23% of the increased temperature over the past 20 years. Perhaps half of this increase is a result of gas released during fracking in the USA and Canada (where 99% of all fracking is taking place). A graph with red dots Description automatically generated Fig. 5 Rise of methane (Parts per billion). **Forests** Just over 10% of anthropogenically released CO~2~ in 2022 was attributed to land use change, notably deforestation. Hence preventing deforestation could make an important contribution to reducing CO~2~. Reforestation might help as well. However, a large amount of land is required to absorb CO~2~ through regenerating forests. We can make this more explicit by considering carbon costs of a flight. Two people making a round trip between Los Angeles and Chicago results in the release about 0.5 tonnes of carbon (really!), which is the same as burning a large tree. To recapture that much over a year requires about 350 growing trees (\~0.7 ha or 1.75 acres). It seems unrealistic to think that planting trees can compensate substantially, at least in the short term. In 2005, the United Nations introduced a "Collaborative Programme on Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (REDD)" as way to slow carbon emissions. The REDD program was originally devoted to funding reforestation. In 2010 the scheme was modified to REDD+, which adds in conservation, i.e., not cutting down trees, as a means of preventing additional carbon release. By 2022, 60 tropical and subtropical countries had REDD+ initiatives. Originally supported by governments, projects associated with carbon sequestration are increasingly funded by corporations to meet climate commitments and engage their stakeholders (often outside the REDD+ framework). The actual effects of these initiatives in reducing deforestation remain controversial, because it is so difficult to know what would have happened in the absence of an agreement. Indeed, many projects have continued to experience at least some deforestation, and loss through fire. A second issue has been that locals cede control of their traditional lands. The international meeting in Glasgow in November 2021 on climate change contained proposals to protect large swathes of land and ocean, raising a concern that this would lead to the usurpation of livelihoods. **Including carbon storage in cost-benefit analyses of the clearing of tropical forests can heavily influence the conclusions drawn from such analyses. One study of tropical woodlands in Paraguay considered benefits in terms of (1) sustainable harvesting of plants and animals, (2) people prepared to pay to search for medicinal plants, and (3) aesthetic values (assessed by the no-use method, of how much people are prepared to pay for conservation of areas even if they themselves will never visit the area). The study then added the additional benefit of carbon**  **Fig. 6. Benefits and costs of conservation across the upper watershed of the Jejuí River in eastern Paraguay. The opportunity cost of conservation is estimated from the cost of purchasing land, which depends on soil quality, topography, and who owns it. Left: The benefit of retaining forest from harvesting and aesthetic value alone. Right: harvesting, aesthetic value, and carbon storage. Black: benefits of conservation outweigh costs. Gray: costs of conservation outweigh benefits. White: not forested nor considered. In the black areas, a park (red) and indigenous areas (green) are already protected, and hence the cost of purchasing the land for conservation is absent or low.** **locked up in trees, which was given a value of \~\$9/tonne of carbon. That valuation is based on (1) estimates of damage expected from climate change and (2) proposed costs under various trading schemes, whereby a polluter can pay someone else to obtain carbon credits. Assuming some organization, such as the United Nations, is indeed prepared to pay this price, carbon storage overwhelms all other benefits at** \$378/hectare/year (2004 dollars, Fig. 6). **T**imber harvest (\$28/ha), existence value (\$25/ha), wild animals for meat (\$16/ha), and prospecting for medicinal plants (\$2/ha) together contribute less than one-fifth in total. When carbon is not included, it appears economically more profitable to convert forest to agriculture. However, when carbon is included, it becomes economically better to purchase forest and preserve it, except in a few places where costs of purchase are high (Fig. 6). **Cap and Trade** Cap and trade programs are emerging, similar to the one described for SO~2~ emissions in an earlier lecture. For example, California has instigated such a program, whereby major consumers and producers of energy (e.g. power plants) have a license to emit a certain quantity of CO~2~ and need to purchase credits to go beyond that level. Those credits are placed on auction, and anyone can buy them. In a program instigated by EPIC (Energy Policy Institute at the University of Chicago), institutions and companies are invited to purchase credits to go "carbon neutral". In an innovative extension, these credits are being advertised across the globe to encourage development of carbon reduction strategies; the credits can be sold back to the auctioneers, and in this way funds for carbon reduction should be generated. **Renewables** Overall, from the above it seems clear that the development of renewables will be essential. The main sources of renewable energy are wind and solar, which now form about 13% of the energy share globally (20% in the USA). Many issues remain, most notably the amount of land required to establish wind farms (as much as 50% of the wind power is taken out by the first line of the wind farm). A recent analysis suggests that with 1.5% of the land in the USA dedicated to renewables, carbon neutrality could be achieved by 2040 through equivalent amounts of solar, wind, nuclear, biofuels and carbon capture techniques. This does come with many assumptions, such as development of more land-efficient biofuels.