Assess different approaches to tackling climate change.

On May 9, 2013, the atmosphere’s CO₂ concentration reached 400 ppm at Mauna Loa Observatory in Hawai‘i. As the summer progressed, it was drawn back down naturally to the high 390s. At the current rate of increase, atmospheric CO₂ concentrations will reach 400 ppm in 2015. It will not drop below that for at least 1,000 years, and probably much longer.

The last time atmospheric CO₂ was at 400 ppm was about 3 million years ago, before the Quaternary ice age began (see Section 6.2). At that time, temperatures were 2°C to 3°C (3.6°F to 5.4°F) higher than today. Global sea level was about 25 m (82 ft) higher than today as a result of less glacier ice.

If anthropogenic CO₂ emissions continue to grow at current rates, CO₂ concentrations will reach 900 ppm by the end of this century (see Figure 6.23A), a concentration that last occurred about 35 million years ago. If CO₂ reaches this concentration, we will face a world that is very different from the world we live in today. How can we avoid this scenario?

One goal set by climate scientists is to reduce CO₂ emissions so that atmospheric CO₂ concentrations do not exceed 500 ppm. Doing so could keep future warming within 2°C (3.6°F). On a global scale, yearly CO₂ emissions would have to be reduced about 80% from current levels, by about 25 billion metric tons, within the next two decades to keep atmospheric CO₂ under 500 ppm.

Reducing the flow of CO₂ to the atmosphere by 80% within two decades is a daunting but technologically achievable goal. Accomplishing it will involve a significant restructuring of the way people produce energy and the way people use fossil fuels. Table 6.2 suggests six specific steps we can take to accomplish this goal. If these six actions were fully implemented, CO₂ emissions would stabilize by 2050 at about 500 ppm. This table is a small sampling of the many actions that can be taken to reduce global carbon emissions.

There is a growing movement to tackle the problem of climate change on a variety of fronts, from the level of the national government to the individual. Environmentally friendly green economies are quickly growing in many countries. A green economy is a sustainable economic system that has a small environmental impact and is based on renewable energy sources.

Coping with increased droughts, floods, disease, sea-level rise, and shifting agricultural zones as a result of changing climate would be far more costly than taking early steps to curb greenhouse gas emissions and preventing serious climate change. Approaches to dealing with the climate problem can be divided into international, local, and individual responses.

International Response

There has been much talk among nations about limiting greenhouse gas emissions. The United Nations Copenhagen Accord in 2009 and the climate change conference in Durban, South Africa, in 2011 were two recent meetings at which the problem was addressed. This work continues with the 2015 climate conference in Paris, where participating nations will agree to legal obligations to cut their carbon emissions. Some 55 nations, which account for 87% of global CO₂ emissions, registered an informal commitment to reduce their greenhouse gas emissions. Canada and the United States, for example, have committed to lowering their CO₂ emissions by 17% from their 2005 emission levels by the year 2020.

National Response

Carbon taxes are seen by many as the most important legislation at the national level to reduce carbon emissions quickly and efficiently. Carbon emissions beyond a predetermined level could be taxed. This would provide an incentive to produce less carbon.

In a similar scheme, carbon cap-and-trade systems allocate carbon “credits” to carbon producers, such as manufacturing companies. A company may purchase more carbon credits from other companies that have carbon credits to sell. Because the overall number of carbon credits is limited, the total carbon emissions of a country would be reduced.

Carbon taxes are politically unpopular. Voluntary reductions and cap-and-trade schemes have thus far been largely ineffective, as evidenced by the upward march of CO₂ concentrations in the atmosphere. One important goal of the next generation will be to establish enforceable and effective legislation to promote greenhouse gas reductions.

Local Response

Half the people in the world live in urban areas, and this percentage is growing. Cities contribute up to 40% of global CO₂ emissions. Over 2,800 cities worldwide have formally committed to reducing their CO₂ emissions. The C40 Cities Climate Leadership Group is a coalition of major cities committed to reducing their greenhouse gas emissions under specific deadlines (Figure 6.25).

Many states have also initiated emissions reduction goals that are voluntary. California, New York, Michigan, Connecticut, and Florida, for example, have set an ambitious goal of reducing greenhouse gas emissions by 80% (relative to 1990 levels) by the year 2050.

Individual Response

The challenge of coping with climate change can seem overwhelming to an individual. Almost all of our daily activities rely on energy from fossil fuels and emit CO₂ into the atmosphere. The average car emits about 5.5 metric tons of CO₂ each year. Heating, cooling, and electricity use in the average house in the United States produce about 11 metric tons of CO₂ each year.

One approach to the problem is to understand your personal carbon footprint. A carbon footprint is the amount of greenhouse gases (particularly CO₂) that any activity generates. There is much literature available on living a low-carbon lifestyle, but the main goal is to reduce greenhouse gas emissions. Many of the steps required to reduce one’s personal carbon footprint call for lifestyle changes (Table 6.3). There are many online “carbon calculators” that allow you to estimate your CO₂ emissions and consider ways to reduce your carbon footprint.

Since the year 1976, every decade has been warmer than the previous one (see Figure 6.17). Atmospheric CO₂ concentrations and temperatures continue to rise. At the same time, green economies and active reduction of carbon emissions are developing a growing momentum. At present, no one yet knows how this planetary-scale unintended experiment will play out.