A Roadmap for Responding to Climate Change

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MIT Alumni for Climate Action*


*The MIT Alumni for Climate Action is a non-partisan group of Massachusetts Institute of Technology alumni concerned about the devastating effects of climate change.


Human activities have increased the concentration of carbon dioxide in our atmosphere from below 300 parts per million (ppm) in the pre-industrial period to over 400 ppm today, which is substantially higher than at any point during human history. The increases in emissions of carbon dioxide and other greenhouse gases are the result of burning fossil fuels and have resulted in the ongoing and observable climate change, including global temperature rise, warming oceans, melting polar ice, glacial retreat, sea level rise, extreme weather events and ocean acidification. The United Nations Intergovernmental Panel on Climate Change (IPCC) assessments have detailed the far-reaching and unprecedented interventions required to limit the worst damages which would otherwise result from climate change. Our recommendation is to develop pathways for a 50-80% reduction in carbon emissions starting immediately and proceeding through the next decade, followed by reaching net-zero greenhouse gas emissions by 2050. Immediate actions necessary include the replacement of coal, petroleum, and natural gas power with carbon neutral (or carbon negative) energy sources, with renewable solar and wind energy holding the most promise. In addition, both significant improvements in energy efficiency and significant reductions in energy use are urgently needed to achieve the climate goals.  Concurrently, careful management of carbon sequestration assets such as forests and agricultural lands is essential. Research and development investments should be aimed at development of a variety of technologies for future uses. For example, the cost of carbon capture needs to be significantly reduced as it is likely to be necessary to reach carbon neutrality through drawdown of atmospheric carbon dioxide. An aggressive timeline is needed to attain the carbon neutrality goals that are needed to avoid the worst damages from climate change that will otherwise occur in the coming decades of the 21st century.

A. Climate change is happening

Prior to the industrial revolution, the concentration of carbon dioxide in our atmosphere varied from 180-300 parts per million (ppm) for hundreds of thousands of years (Figure 1). Due to the burning of fossil fuels, especially since World War II, the concentration of carbon dioxide has been increasing steadily from preindustrial levels. Recently, the concentration of carbon dioxide has risen to over 400 ppm, which is substantially higher than at any point during human history. With the growth of the world’s human population to over 7 billion and industrialization around the world using fossil fuels, the concentration of carbon dioxide is expected to double in the next several decades and reach 1,000 ppm (0.1 %) in the late 21st or early 22nd century. Such a rapid increase in carbon dioxide, a greenhouse gas, is contributing to the increase in the global mean temperature of the atmosphere (Figure 2). Atmospheric carbon dioxide and other greenhouse gases primarily from burning fossil fuels are leading to ongoing and observable climate change, including global temperature rise, warming oceans, melting polar ice, glacial retreat, sea level rise, extreme weather events, and ocean acidification.

The changes that are ongoing as a result of human activities are unprecedented and historic. The last time carbon dioxide concentration was at current levels was more than 3 million years ago, when the world’s temperature was 2-3°C higher than today and the sea level was 15-25 meters higher. With business as usual, the United Nations Intergovernmental Panel on Climate Change (IPCC) assessments have detailed the far-reaching and unprecedented damages to the world’s environment and ecosystems. The IPCC has also provided the responses required to avoid this fate. The most important among them is limiting emissions of carbon immediately, through reduction in greenhouse gas combustion, which will lead to lessening global warming, and ensure a more sustainable world with clear benefits to people and natural ecosystems. The longer is the delay in action, the more difficult the problems will be to address in future.

Figure 1. (Left) Atmospheric carbon dioxide concentration (Y-axis in parts per million, ppm) versus time 500,000 years before present (x-axis in years prior to present). 

Figure 2. (Right) Global mean temperature 1950-2020 (5-year averages) plotted in oC (y-axis) versus years (x-axis).

Climate change is an undeniable fact. At the end of the second decade of the 21st century, it is sobering to review some of the monumental records recently set around the world. A recent report from NASA and NOAA found that the past five years each ranked as the five hottest on record globally similar to 19 of the past 20 years in this century. At the start of 2020, January has already been the hottest on record in Europe, 3.1 °C warmer compared to a 1981-2010 baseline, with parts of the northeast of the continent extraordinarily (6.1 °C) warmer. In addition, a new record high was recently reported on the continent of Antarctica, 20.7 °C, beating the previous record of 18.3 °C set a few weeks earlier. Meanwhile, in Australia, after experiencing the driest spring on record in 2019, the country recently recorded its hottest day ever, with an average high of 41.9 °C (107.4 °F), which was 1 °C higher than the record set the previous day.

All of these temperature records are fueling destructive weather events in 2020, for example increasing wildfires around the world chronicled in a Science Brief report. The exceptionally dry and hot Australian summer has led to the worst wildfire season ever, with an area larger than Austria burned. Extreme summer temperatures and strong winds also resulted in wildfires near Valparaiso, Chile, similar to what we saw again last year in California. In the Mediterranean region, "Medicanes" such as Gloria flooded a river delta in eastern Spain and they are occurring more frequently. Closer to home, five winter tornadoes were reported in the Washington DC region during a recent unnamed storm. The worldwide effects of extreme weather events as a result of climate change are so concerning that the headline of a recent opinion column in the New York Times was: "Apocalypse Becomes the New Normal".

The long-term effects on the forests and oceans of the world, buffers against global catastrophe from climate change, suggest that the world is quickly progressing toward a tipping point. The unrelenting and deliberate burning of the Amazon may be pushing 'the lungs of the world' to a point where corrective action may no longer be possible. The Greenland ice sheet is losing unprecedented amounts of ice with an ever increasing contribution to global sea-level rise. Studies of Antarctic glaciers are on-going, and early results suggest that these are contributing even more substantially to sea-level rise. Another study of ocean currents recently concluded that substantial acceleration in global ocean circulation has occurred in the past few decades, intensified by surface winds and reaching kilometer depths. All of these are the result of climate change leading to record high temperatures of the oceans, which were the hottest ever in 2019, and before that in 2018, and before that in 2017, a disturbing repeating trend on a global scale.

Climate change from ongoing greenhouse gas emissions is clearly happening and is an increasing threat to humans. Climate hazards are a threat not only to human health, water, and food, but also to our economy, infrastructure, and security. Without immediate action to aggressively reduce emissions, the world will be regularly exposed to multiple concurrent hazards. Estimates are that by the year 2100,  there will be from three to six simultaneous events, posing a broad threat via the intensification of the multiple vulnerabilities of humanity. Moreover, continuation of current trends without immediate action is expected to result in upwards of 1-3 billion climate refugees in the next 50 years.

B. Immediate action is needed to address the challenges of climate change

(Add introductory paragraph) The following seven actions represent necessary priorities:

1. Aspire to make the world carbon-neutral within a generation. “Carbon-neutral” means no net addition of greenhouse gases in the atmosphere. The sooner this aspirational goal is achieved, the less damage will be experienced in the future. Action at all levels will be needed to ensure success, from elected leaders to ordinary citizens and businesses. We should commit to making significant greenhouse gas reductions by 2030 so that we will be on a path to become carbon neutral by 2050 through legislation and personal actions.

2. Replace fossil fuel power generation with carbon-free energy. Immediately accelerate the replacement of fossil fuel plants with renewable wind and solar power, rapidly move towards the development of off-shore wind power capability, and expand commercial solar photovoltaic capability. On-shore wind and rooftop residential, government and commercial solar installations should also be expanded.

3. Build more efficient transportation systems. Expand and expedite the transition to electric vehicles, mass-transit and low-carbon transportation solutions such as light rails and subways. This may be accomplished by extending tax credits to all high mileage vehicles, including hybrids. Electric vehicle charging infrastructure should be incentivized in homes, fueling stations, garages, and workplaces to facilitate transition away from gasoline and diesel powered vehicles.

4. Invest in efficient buildings and communities. Move rapidly to the development of energy efficient buildings and communities. New construction should include smart, efficient materials, renewable energy sources and electric vehicle chargers. The world’s research enterprise must be encouraged to find technical solutions to climate change problems, including smart grids, improved energy storage, and expanded liquid biofuels.

5. Expand carbon capture. Improve management of agricultural and forest lands to increase their capacity for carbon capture, which will also improve our air and water quality, and promote better health. Prevent the destruction of the Amazon and the world’s great forests. Ultimately, increased carbon capture is likely to be necessary to realize carbon neutrality through drawdown of atmospheric carbon.

6. Incentivize our citizens and businesses. Put a price on carbon and expand programs to cap carbon emissions to shrink our carbon footprint rapidly. In order to achieve the goal, phased revenue neutral carbon pricing legislation is necessary, with mandated increases in the commitment of utilities to renewable energy and incentivizing fuel-efficient cars, trucks and appliances, and less wasteful lifestyles for our citizens.

7. Protect public health. Develop effective plans to respond to the adverse public health consequences of climate change, including managing extreme weather events such as in expanding flood zones, and addressing health concerns from increased temperatures, ozone, asthma, allergies, and infectious diseases. Management of vulnerable communities likely to suffer the worst effects of flooding and storms, including poorer citizens and minorities, must be prioritized.

C. Pathways to mitigate greenhouse gas emissions and sequester atmospheric CO2

The MIT Alumni for Climate Action strongly supports the aspirational goal to make the world carbon-neutral within a generation. This goal is consistent with the IPCC target for limiting global warming to less than 2oC to prevent the worst of the damages. The U.S. commitment to the Paris Agreement’s Nationally Declared Contribution (NDC) was to reduce greenhouse gas emission reductions by 26-28% by 2025 (Figure 3), and increase these targets are needed for COP26 to limit global warming to the desired IPCC goals. To make this happen, we encourage elected representatives in both the U.S. government and the individual states to immediately pass legislation that commits governments to achieve net-zero greenhouse gas emissions by 2050 or earlier. We believe that this goal can be achieved by a combination of improvements in energy efficiency, reductions in energy demand, electrification of most fossil fuel usage, and by capturing and sequestering carbon dioxide from the atmosphere.

Figure 3. United States NDC emissions targets for 2020 and 2025 in the Paris Agreement.

Even though the net-zero goal is very ambitious and not all of the needed technologies are currently available, we are confident that by setting the appropriate goals and funding the necessary research that our society will be able to meet the challenge. Many states, including California, Washington, Hawaii, New York, New Jersey, Maryland, and others initially set an intermediate goal of ~50 % reduction in emissions by 2030, which is achievable by use of current technologies and puts us on the pathway to net-zero by 2050. The state of California has set an example by committing to net-zero greenhouse gas emissions in 2045 (see LLNL report). Although each state has its own unique circumstances, the broad outline of California's approach is applicable to most (if not all) states and for the United States as a whole. However, since not all states have the same relative resources or emissions, the US government may need to offer assistance to individual states on a case-by-case basis.

The methodology for getting to net-zero greenhouse gas emissions involves the following steps: (1) do an inventory of current greenhouse gas emissions; (2) develop an emissions pathway for 2020 to 2050; (3) determine a realistic greenhouse gas emissions budget; (4) develop a plan for reducing greenhouse gas emissions; and (5) develop a plan implementing sufficient negative emission technologies to become “carbon neutral”.

1. Inventory of Current Greenhouse Gas Emissions. There are about 60 major sources of greenhouse gas emissions (source Energy Information Agency-EIA). Table 1 lists the top 12 sources of greenhouse gas emissions that together are responsible for nearly 80% of all emissions in the U.S.  The top sources are from the use of coal, petroleum, and natural gas for electricity and transportation for residential industrial sectors, and from agricultural activities.

Table 1. Top Sources of US Greenhouse Gas Emissions in 2018

2. Development of 80% Emissions Reduction Pathway.
The simplest way to create an emissions reduction pathway is to assume that emissions will be reduced linearly from 2020 amounts to 80% of 2020 amounts in 2050. Policies can then be created to reach intermediate goals of 50 % or higher. About 20% of greenhouse gases emissions will be more difficult to eliminate (California is planning on emissions being cut by 80% by 2045 - see Figure 4), research and development are necessary to reach the aspirational goal of carbon neutrality while intermediate goals are immediate targets.

Figure 4. California Emission Reduction Trajectory (Source: LLNL)

3. Greenhouse Gas Emissions Budget. Several ways to calculate the U.S. budget for a global temperature increase of 1.5°C are shown in Table 2 (U.S. greenhouse gas emissions in 2017 were 6.47 GTCO2e). For most states, the per-capita greenhouse budget will be the same as that for the US as a whole (with a possible adjustment depending on the state's circumstances).

Table 2. Proposed U.S. Greenhouse Gas Emission Budgets

4. Reducing Greenhouse Gas Emissions. There are three primary ways to mitigate greenhouse gas emissions: (a) replace fossil fuel usage for energy with carbon-free energy (or capture the CO2 produced by the burning of fossil fuels), (b) increase energy efficiency, and (c) reduce/alter consumption. Table lists some of the actions that can be taken to reduce emissions and includes both an estimate of the emissions reductions for the U.S. and how the reductions compare to the overall goal of an 80% reduction of 2020 emissions by 2050. 

Since market forces will determine which of the carbon-free  technologies will be used to replace fossil fuels for the production of electricity, it is very difficult to estimate how much capacity will increase for the various technologies. Instead the costs and potential for each technology is estimated.

Table 3 Fossil fuel uses that need to be addressed to meet 80% reduction target

5. Negative Emission Technologies. We have long past the point where we can limit the temperature increase to even 2°C by mitigation alone - even with a carbon tax we won't be able to both reduce consumption and promote carbon-free electricity fast enough to keep the atmospheric concentration of greenhouse gases at the required level. Because of this, significant amounts of CO2 (likely hundreds of gigatons) will need to be removed from the atmosphere this century.  If U.S. emission reductions start in 2020 (on a linear path to an 80% reduction of 2020 emissions in 2050), the "annual negative emissions requirement" will be about 2 GTCO2.  Assuming  a cost of $100/ton for removing CO2 from the atmosphere, this would result in an annual cost for carbon removal  of about $200 Billion (roughly $500/person per year). Every year of delay adds about 100 MTCO2 to the needed annual carbon capture and storage at an incremental cost of about $10 Billion/year ($25/per person/year).  Note that U.S. GDP will be increasing by about $500 BIllion/year over the next 10 years. This means that, from a strictly economic point of view, there is no urgency to carbon neutrality as we'd be passing on only slightly higher costs to future generations where the GDP is increasing much faster than the increased costs.  The real costs of delay are (1) the very likely increase in CO2-equivalent emissions from natural feedbacks (which would need to be compensated for with additional CO2 capture), and (2) additional costs from increased weather-related economic damages.

For an individual state, the quantity of negative emissions that will be required can be calculated by subtracting the  "state greenhouse gas budget" from the states "gross greenhouse gas emissions".  Table 4 lists some examples of negative emission technologies.

Table 4 - Examples of Negative Emission Technologies

Concluding statement

Disruptive transformation to renewable energy is ongoing but a greater sense of urgency is needed to prevent the worst damages which will otherwise result from climate change, which include global temperature rise, warming oceans, melting polar ice, glacial retreat, sea level rise, extreme weather events, and ocean acidification. Current public opinion is overwhelmingly in support of transitioning to renewable energy, both in the US and worldwide and should be transformed into legislation and public policy as soon as possible. The levelized cost electricity from renewable energy is becoming lower than fossil fuels and more competitive, which will naturally move the world toward carbon neutrality. However, the rate at which this occurs will determine the long-term damages which will result. Given the technological capabilities of the US and its historic contribution to greenhouse gas emissions, it should take a leadership position in this sustainability revolution. Rapid progress toward climate neutrality will benefit all of the world’s citizens and future generations and should not be hindered by other extraneous factors.

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