Ice Properties, Sea Ice, and Milankovitch Cycles

Ice shares many similarities with snow.
High Albedo: Ice has a high albedo (50-60%), although snow can have an even higher albedo (up to 95%). Albedo is the measure of how much light that hits a surface is reflected without being absorbed.
High Emissivity: High emissivity helps keep the surface cool. Emissivity is the measure of an object's ability to emit infrared energy.
Good Insulator: Ice insulates the warm ocean/water beneath it.
High Specific Heat Capacity: As ice melts, its high specific heat capacity helps cool the planet and ocean. Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.
Melting Characteristics: Ice melts slowly, absorbing latent heat and contributing to climate stability. Latent heat is the heat required to convert a solid into a liquid or vapor, or a liquid into a vapor, without change of temperature.

Density: Ice density is slightly lower than that of water, approximately $920 kg/m^3$ (92% of water's density).
Floating Ice: Due to its lower density, ice floats on water, forming a layer on top of lakes and seas during winter. The typical depth of ice is around 50 cm on lakes and about 1 meter on the sea. Floating ice doesn't really raise sea-level.
Expansion Upon Freezing: When water freezes, it expands, causing the lake/sea surface to be much higher in winter than in summer.
Sea Level Impact: Melting floating ice (on the Arctic or on lakes) does not significantly raise sea levels.
Ice Shelf vs. Ice Sheet Contrast: Melting sea ice does not raise sea levels in the same way that melting ice sheets do.
Ice on Land: Ice sheets on land, when they melt and flow into the sea, will raise sea levels.

Maximum Water Density: The densest water is at 4°C. This means the bottom of a lake is 4°C, preventing it from freezing and allowing life to survive in the Arctic Ocean and lakes.
Salinity Influence: Salinity affects water density; saltwater is more dense.

Potential Disruption: Increasing melt from ice shelves and ice sheets could disrupt the thermohaline circulation.
Mechanism: Saltwater is denser than freshwater. Increased ice melt results in fresher (less dense) water, which is less likely to sink as North Atlantic Deep Water (NADW), potentially turning off the conveyor belt-like circulation.
Reference Link: http://www.geog.ucl.ac.uk/~jfogarty/GCM_essay.html

Past Ice Sheet Coverage: Maps illustrate the extent of ice sheets 18,000 years Before Present (BP), covering large parts of North America (Laurentide Ice Sheet, Cordilleran Ice Sheet) and Eurasia (Eurasian Ice Sheet).

Explanation: Milankovitch Theory explains long-term changes in Earth's climate due to variations in Earth's orbit.
Eccentricity:
- Description: Changes in the shape of Earth's orbit (more or less elliptical).
- Periodicity: Approximately 100,000 years.
Axial Tilt (Obliquity):
- Description: Variations in the angle of Earth's axial tilt.
- Periodicity: Approximately 41,000 years.
Precession:
- Description: Wobble in Earth's axis of rotation.
- Periodicity: Approximately 23,000 years.
Combined Effect: The combined effect of these cycles is to redistribute energy input across Earth.

Energy Input: The total amount of radiation received by Earth in a year stays the same overall.
Amplification by Snow and Ice: Snow and ice amplify the effects of these cycles.
Ice Age Initiation: In a hemisphere with lower summer solar input and higher winter solar input, snow does not melt, and ice sheets develop, initiating an ice age.
Northern Hemisphere Dominance: The Northern Hemisphere plays a dominant role in these processes.
Positive Feedback Loop: Operates in both cooling and warming directions.
- Cooling: Less surface heating leads to reduced melting, more ice, and increased albedo.

Rapid Melting: The Greenland Ice Sheet is currently melting very rapidly.
Sea Level Rise Equivalent: Contains the equivalent of 7.2 meters of sea level rise.
Sea Level Rise Prediction: Predicts 5-33 cm of sea level rise by 2100 (Aschwanden et al. 2019).
RCP Scenario Dependence: The exact change depends on the Representative Concentration Pathway (RCP) scenario.
Thermohaline Circulation Disruption: The melting may already be disrupting the thermohaline circulation (though this is controversial).
Source: https://www.manchester.ac.uk/discover/news/scientists-chart-history-of-greenland-ice-sheet-for-first-time/
Source: https://advances.sciencemag.org/content/5/6/eaav9396