The air bubbles trapped in mile-thick ice cores and other paleoclimate evidence suggests that during the ice age cycles of the past million years or so, the atmospheric carbon dioxide had never exceeded 300 ppm. Before the Industrial Revolution started in the mid-1700s, atmospheric carbon dioxide was 280 ppm or less.
The amount of carbon dioxide in the atmosphere has increased along with anthropogenic emissions since the Industrial Revolution in 1750. Emissions rose slowly to about 5 billion tons per year in the mid-20th century before skyrocketing to more than 35 billion tons per year by the end of the century. This connotes the significance of anthropogenic factors in intensifying the atmospheric concentration of carbon dioxide in the recent century.
The figure below shows the plausible future socioeconomic pathways for annual carbon dioxide emissions and the resulting atmospheric carbon dioxide concentrations through the end of the century.
If global energy demand continues to grow rapidly and we meet it mostly with fossil fuels, human emissions of carbon dioxide could reach 75 billion tons per year or more by the end of the century. Atmospheric carbon dioxide could be 800 ppm or higher—conditions not seen on Earth for close to 50 million years. (Chemistry) (STEM)
Conversely, the atmospheric carbon dioxide will greatly be minimized in the scenario of SSP 1-1.9, i.e., energy production dominated by renewable energy, which is a clean source of energy that do not have carbon emissions. This implies the importance of a clean electricity mix in controlling anthropogenic carbon emissions. (Chemistry) (STEM)
SSP1 |
Sustainability – Taking the Green Road (Low challenges to mitigation and adaptation) The world shifts gradually, but pervasively, toward a more sustainable path, emphasizing more inclusive development that respects perceived environmental boundaries. Management of the global commons slowly improves, educational and health investments accelerate the demographic transition, and the emphasis on economic growth shifts toward a broader emphasis on human well-being. Driven by an increasing commitment to achieving development goals, inequality is reduced both across and within countries. Consumption is oriented toward low material growth and lower resource and energy intensity. |
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SSP2 |
Middle of the Road (Medium challenges to mitigation and adaptation) The world follows a path in which social, economic, and technological trends do not shift markedly from historical patterns. Development and income growth proceeds unevenly, with some countries making relatively good progress while others fall short of expectations. Global and national institutions work toward but make slow progress in achieving sustainable development goals. Environmental systems experience degradation, although there are some improvements and overall the intensity of resource and energy use declines. Global population growth is moderate and levels off in the second half of the century. Income inequality persists or improves only slowly and challenges to reducing vulnerability to societal and environmental changes remain. |
SSP3 |
Regional Rivalry – A Rocky Road (High challenges to mitigation and adaptation) A resurgent nationalism, concerns about competitiveness and security, and regional conflicts push countries to increasingly focus on domestic or, at most, regional issues. Policies shift over time to become increasingly oriented toward national and regional security issues. Countries focus on achieving energy and food security goals within their own regions at the expense of broader-based development. Investments in education and technological development decline. Economic development is slow, consumption is material-intensive, and inequalities persist or worsen over time. Population growth is low in industrialized and high in developing countries. A low international priority for addressing environmental concerns leads to strong environmental degradation in some regions. |
SSP4 |
Inequality – A Road Divided (Low challenges to mitigation, high challenges to adaptation) Highly unequal investments in human capital, combined with increasing disparities in economic opportunity and political power, lead to increasing inequalities and stratification both across and within countries. Over time, a gap widens between an internationally-connected society that contributes to knowledge- and capital-intensive sectors of the global economy, and a fragmented collection of lower-income, poorly educated societies that work in a labor intensive, low-tech economy. Social cohesion degrades and conflict and unrest become increasingly common. Technology development is high in the high-tech economy and sectors. The globally connected energy sector diversifies, with investments in both carbon-intensive fuels like coal and unconventional oil, but also low-carbon energy sources. Environmental policies focus on local issues around middle and high income areas. |
SSP5 |
Fossil-fueled Development – Taking the Highway (High challenges to mitigation, low challenges to adaptation) This world places increasing faith in competitive markets, innovation and participatory societies to produce rapid technological progress and development of human capital as the path to sustainable development. Global markets are increasingly integrated. There are also strong investments in health, education, and institutions to enhance human and social capital. At the same time, the push for economic and social development is coupled with the exploitation of abundant fossil fuel resources and the adoption of resource and energy intensive lifestyles around the world. All these factors lead to rapid growth of the global economy, while global population peaks and declines in the 21st century. Local environmental problems like air pollution are successfully managed. There is faith in the ability to effectively manage social and ecological systems, including by geo-engineering if necessary. |
The chart below compares the projected warming under similar emissions secnarios in AR5 and AR6 reports.
Both AR5 and AR6 reports suggest that the continuation of electricity mix that relies solely on fossil fuel combustion will result in the greatest warming rate, while that of renewable energy will accomplish sustainability with the lowest growth in warmth rate. (Chemistry) (STEM)
**Increase in mean and increase in variance will end up more often extereme hot waether
A case study of USA: Huge increase in the intensity and frequency of heat days and heatwaves in the recent decades, which intensifies natural hazards and results in more hospitalization due to heat-related illnesses, such as respiratory disorders and heat stroke. (Geography Sustainable Cities)
Increasing variability and unevenness in rainfall / precipitation among regions as a result of increasing global temperature.