D4.3.1—Anthropogenic causes of climate change

• Greenhouse Effect: The Earth’s atmosphere traps heat from the sun, similar to how a car parked in the sun gets hot. This is known as the greenhouse effect.
• Greenhouse Gases: Methane and carbon dioxide are key greenhouse gases.
• Human Activities: Burning fossil fuels (like coal, oil, and gas) and deforestation are major sources of greenhouse gas emissions.
• Global Warming: Increased greenhouse gases trap more heat in the atmosphere, leading to a rise in global temperatures.
• Climate Change Impacts: This warming affects weather patterns, including increased frequency and intensity of extreme weather events.

D4.3.2—Positive feedback cycles in global warming

Key Points:

• Melting Ice and Albedo: Snow and ice have a high albedo, meaning they reflect a lot of sunlight back into space. As polar ice and sea ice melt, more of the Earth’s surface is exposed, which absorbs more heat. This leads to further warming and accelerated ice melt.
• Permafrost Melting: Permafrost contains large amounts of organic matter. As permafrost thaws due to rising temperatures, this organic matter decomposes and releases methane, a potent greenhouse gas. This further contributes to warming and accelerates permafrost thaw.
• Ocean Warming and Carbon Dioxide Release: As global temperatures rise, the temperature of the oceans also increases. Warmer water can hold less dissolved carbon dioxide. This leads to the release of more carbon dioxide from the oceans into the atmosphere, further amplifying warming.

These positive feedback cycles create a self-reinforcing process where warming leads to changes that accelerate further warming. They are a significant concern as they can make it more difficult to mitigate the effects of climate change.

D4.3.3—Change from net carbon accumulation to net loss in boreal forests as an example of a tipping point

• Tipping Point in Boreal Forests: Climate change is causing warmer and drier summers in boreal forests. This increases the frequency and severity of wildfires.
• Carbon Release: These fires release large amounts of carbon dioxide stored in the forest’s detritus (dead organic matter).
• Reduced Carbon Storage: Wildfires also damage the forest’s ability to store carbon by killing trees and disrupting the ecosystem.
• Shift to a Carbon Source: This combination of factors could lead to a tipping point where boreal forests transition from being a carbon sink (absorbing more carbon than they release) to being a carbon source (releasing more carbon than they absorb).
• Ecosystem Shift: After fires, deciduous forests with trees spaced farther apart may replace the original boreal forest, further altering the ecosystem’s carbon cycle.

D4.3.4—Melting of landfast ice and sea ice as examples of polar habitat change

It explains how the melting of landfast ice and sea ice is impacting the habitats of polar animals, particularly emperor penguins and walruses.