Natural Climate Change

Summary

This lecture delves into natural climate change, focusing on the key factors influencing Earth's climate. It covers solar variability, including sunspot activity and its uncertain relationship with temperature changes. The Earth’s orbital cycles, known as Milankovitch cycles, and their long-term effects on climate are explored. The role of continental movement, atmospheric gases, and aerosols, such as those released by volcanic eruptions, is also discussed. Additionally, the concept of climate feedbacks, like the ice-albedo feedback, is highlighted, explaining how melting ice contributes to further warming through positive feedback loops.

Takeaways

• 😀 Solar variability is the main driver of natural climate change, with the Sun's energy output varying over different time scales, impacting Earth's climate.
• 😀 Sunspots, though cooler than other areas on the Sun, are linked to higher solar output and potentially higher temperatures, but the full mechanism is not yet understood.
• 😀 Earth's orbit undergoes changes on long cycles, including variations in orbital shape, axis wobble, and tilt, which influence climate patterns over tens of thousands of years.
• 😀 Milankovitch cycles, referring to Earth's orbital and axial variations, have a significant role in glacial and interglacial cycles.
• 😀 Plate tectonics, through the movement of continents, also plays a vital role in climate by affecting atmospheric and oceanic circulation patterns.
• 😀 The closing of the Panamanian land bridge redirected ocean currents, creating the Gulf Stream, which significantly warms Europe's climate.
• 😀 Natural processes like volcanic eruptions release gases such as CO2, which contribute to warming, but volcanic aerosols can temporarily cool the climate by increasing Earth's albedo.
• 😀 Volcanic aerosols can lead to cooling by reflecting sunlight away from Earth, causing temporary drops in temperature.
• 😀 Climate feedbacks, such as the ice-albedo feedback, amplify trends of warming or cooling. The melting of sea ice reduces albedo, leading to more heat absorption and further melting, creating a positive feedback loop.
• 😀 The Arctic's melting sea ice, which lowers Earth's albedo, exemplifies a positive feedback mechanism, accelerating the warming trend as the ice is replaced by darker ocean water.

Q & A

What are the two main types of climate change processes discussed in the script?

The two main types of climate change processes are natural and anthropogenic (human-caused) processes.

How does solar variability impact the Earth's climate?

Solar variability, which refers to changes in the Sun's energy output, affects the Earth's climate by influencing temperature patterns. Over various time scales, such as decades and thousands of years, changes in solar output, such as sunspot activity, are linked to temperature variations on Earth.

What is the relationship between sunspots and solar output?

Sunspots are dark spots on the Sun's surface caused by magnetic field variations. Although sunspots themselves are cooler than the rest of the Sun, higher sunspot activity tends to correlate with higher solar output and, often, warmer temperatures on Earth.

What are Milankovitch cycles, and how do they influence Earth's climate?

Milankovitch cycles refer to three variations in Earth's orbital patterns: changes in orbit shape (eccentricity), axial tilt, and axial wobble. These cycles influence the Earth's distance from the Sun and the orientation of its hemispheres, contributing to long-term climate changes, including glacial and interglacial periods.

How does the position of continents affect climate?

The position of continents influences atmospheric and oceanic circulation, impacting climate. For example, the closing of the Panamanian land bridge redirected ocean currents, such as the Gulf Stream, which warmed Europe by about 18°C.

What is the role of volcanic eruptions in natural climate change?

Volcanic eruptions release gases and aerosols into the atmosphere. While volcanic gases like CO2 can contribute to warming, aerosols increase Earth's albedo, reflecting sunlight and leading to a cooling effect. Large eruptions can cause temporary cooling for months or years.

What is albedo, and how does it affect Earth's climate?

Albedo refers to the reflectivity of a surface. Lighter-colored surfaces, like ice, have higher albedo, reflecting more sunlight and cooling the climate. Darker surfaces, like water, absorb more sunlight, which can lead to warming.

What is the ice-albedo feedback, and how does it contribute to climate change?

The ice-albedo feedback is a process where melting ice, which has high albedo, exposes darker surfaces, like water, with lower albedo. This causes more sunlight to be absorbed, further warming the region and causing more ice to melt, creating a positive feedback loop.

How do Earth's orbital cycles (Milankovitch cycles) impact the timing of glacial and interglacial periods?

Milankovitch cycles, including changes in Earth's orbital shape, axial tilt, and wobble, influence the Earth's climate over tens of thousands to hundreds of thousands of years, contributing to the onset and end of glacial (ice age) and interglacial (warmer) periods.

Why is the current warming of the Earth not caused by changes in solar output?

While solar variability does influence Earth's climate, scientists agree that the changes in solar output observed in recent years are not responsible for the current warming trend. The primary cause of current warming is anthropogenic factors, particularly the increase in greenhouse gas emissions.