Chapter 3D Main ideas

1. Human influence on the Climate

Humans likely began influencing the climate when change from hunter-gatherer to agricultural societies began. The more drastic impact of humans on the climate began with the Industrial Revolution and increased use of fossil fuels. The carbon isotope signature of atmospheric CO₂ is used to measure anthropogenic emissions from burning fossil fuels and anthropogenic emissions do not have an equivalent sized sink in the carbon cycle.

2. Modeling Earth’s Climate

Climate models are computer simulations based on known physical interactions in the Earth system and are used to project how changing greenhouse gas emissions will affect future climate conditions on the planet. Current models use a combination of possible social/economic/political/technological changes (Shared Socioeconomic Pathways) coupled with mitigation targets to create climate projections through the year 2100.

3. Modern and Projected Consequences of Climate Change

The planet is already experiencing changes as a result of climate change. Models create projections of how greenhouse gas emissions, atmospheric greenhouse gas concentrations, temperature, droughts, storms, ice, snow, permafrost, sea level, ocean pH, habitat biomes, invasive species, forests, and human health (among other factors) will change with varying future scenarios. It is clear that keeping temperature rise to a minimum, 1.5°C, will mean far fewer harmful impacts to the human and natural world.

4. Climate Mitigation

From an economic standpoint, it is less expensive to invest in efforts to reduce atmospheric CO₂ than what is spent on the current social cost of carbon. Mitigation efforts include reducing greenhouse gas emissions through more renewable energy, better agricultural practices, etc. and increasing the removal of CO₂ from the atmosphere through more wetlands and forests and through manmade technologies that capture atmospheric carbon. The current mitigation efforts must be increased dramatically over the next decade if we hope to keep the planet from warming more than 1.5°C by 2100.