In these questions you are asked to consider some possible future scenarios for atmospheric greenhouse gas accumulations. To start, go to co2.earth and find the most recent monthly CO2 measurement. Round your answer to a whole number.

CO2: ____________ ppm

The units for the measurement of CO2 in the atmosphere are ppm, or parts per million this indicates the total amount of CO2 existing in the atmosphere.

This website also indicates CO2 levels for the last few years. Using past years of CO2 levels, find the yearly rate of increase for CO2 levels. In other words, how much CO2 was emitted to the atmosphere in the past year? Round your answer to a whole number.

CO2 emissions: _____________ ppm/year

Make sure you note the difference between the amount of CO2 in the atmosphere (ppm) and the emissions (amount added each year) of CO2 to the atmosphere (ppm/year). (The amount should be a number in the hundreds and the emissions should be a single digit number.)

Now let’s consider some scenarios for the future. Right now, human population is just over 8 billion people. Those 8 billion people together are producing the yearly emissions of CO2 which you specified above. If there are more people, more CO2 would be emitted to the atmosphere. What is human population expected to be in 2050? (Use text or internet to find your answer.)

2050 human population: _____________ billions

Now calculate how much CO2 that many people would emit each year, assuming no other changes.

2050 human population * 2024 emissions = 2050 emissions 2024 human population

CO2 emissions in 2050: ___________ ppm/year

Of course, it’s unlikely that nothing else besides population would change. In recent years, for instance, a major global change has been the steadily increasing number of people who are able to live the middle-class lifestyle and levels of consumption that are typical in the United States. Those middle-class lifestyles and consumption levels are responsible for the bulk of CO2 emissions people living at subsistence levels are contributing negligible amounts of CO2 to the atmosphere. So let’s consider the additional change that would result from more people living life in the middle class. Right now, about 2 billion of the world’s population is in the middle class – by 2050, about 4 billion people will live in middle class circumstances and CO2 emissions should be expected to increase proportionally.

2050 middle class population * 2024 emissions = 2050 emissions 2024 middle class population

Middle-class CO2 emissions in 2050: __________ ppm/year

Our goal now is to determine what CO2 levels should be expected by the year 2050, with the yearly emissions we have determined. An accurate calculation should use calculus but we will assume that the rate of increase is uniform, so that we can use the average emissions over the entire period 2024-2050. Find the average of these two values, emissions today and expected middle-class emissions in 2050.

Average of CO2 emissions in 2024 and in 2050: __________ ppm/year

Now find the total amount of CO2 which will be added to the atmosphere between now and 2050, by multiplying average emissions by the number of years.

Total CO2 emissions in the period 2024-2050: __________ ppm

Add that amount to the CO2 levels present in the atmosphere now.

2050 atmospheric CO2 levels: __________ ppm

(Your answer to the last question should be in the hundreds, not thousands or tens of thousands. If it is not in the hundreds, go back to find your mistake.)

Now let’s consider a somewhat more optimistic scenario. Numerous changes to our energy infrastructure are being made, albeit slowly. If all coal-burning power plants were converted to burning natural gas, electricity emissions would be approximately cut in half. If all vehicles were modified to run off electricity or natural gas, transportation emissions could also be cut by about a third. Currently in the U.S., generation of electricity accounts for 33% of CO2 emissions and transportation accounts for 28% of CO2 emissions. If we assume that both generation of electricity and transportation were to be completely converted to natural gas by 2050, we can calculate the reduction in CO2 emissions which would result.

Reduction of electricity emissions would amount to a 17% reduction in total CO2 emissions, and reduction of transportation emissions would amount to a 9% reduction in total CO2 emissions. Taking the two together would be an emissions reduction of 26%, or about one-fourth. We must also take into consideration, however, the fact that changes cannot be made all at once. Assuming that it takes most of the time 2024-2050 to make these changes, we can approximate their effect over the entire time by cutting the reduction in half. Find the reduced total CO2 emissions, using the total emissions from above reduced by 1/8. (Reducing by 1/8 means subtracting 1/8 of the original amount, or calculating 7/8 of the original amount.)

Reduced total CO2 emissions in the period 2023-2050: __________ ppm Add that reduced amount to the CO2 levels present in the atmosphere now. Reduced 2050 atmospheric CO2 levels: __________ ppm

Now we have calculated a pessimistic and an optimistic estimate of how much CO2 might exist in Earth’s atmosphere in 2050. Keep in mind what CO2 levels to compare that to: in the last million years, atmospheric CO2 has only ever fluctuated between 200 ppm and 300 ppm.