Glacial/interglacial Cycles

Ok so i didn’t separate the sections well enough now THIS is the final part. Part 11.

When was the last ice age (Last Glacial Maximum)? How much colder was global average temperature? What was the difference in sea level? What was the atmospheric CO2 concentration?When was the last ice age (Last Glacial Maximum)? How much colder was global average temperature? What was the difference in sea level? What was the atmospheric CO2 concentration?

The last ice age peaked at the Last Glacial Maximum around 21,000 years ago

Global average temp was 4-5 degrees colder

Sea level was approximately 120 meters lower

Atmospheric CO2 concentration was around 180-200 ppm

In the past, has the Earth been as warm as it is today? Has CO2 been as high as it is today? How did changes in temperature and CO2 in the past compare to recent changes?

In the past, Earth has been as warm as today, but CO2 levels have not been as high as they are currently.

Changes in temperature and CO2 levels in the past have occurred over longer timescales compared to recent changes, which have been more rapid.

Role of CO2 in climate change

CO2 acts as a greenhouse gas, trapping heat in earth’s atmosphere and contributing to the greenhouse effect

Increased CO2 levels from human activities enhanced the greenhouse effect, leading to global warming and climate change

CO2’s role in climate change is central, amplifying temperature increases and driving feedback loops that further influence earth’s climate system

What is the function of a greenhouse gas (how is it different from other gases)?

Greenhouse gases trap heat, warming the atmosphere

What was atmospheric CO2 concentration (in ppm) at: the last ice age (for glacial periods over the last 800 kyrs), during interglacial (warm) periods over the last 800 kyrs, at pre-industrial times around 1800), today?

Last ice age (180-200 ppm)

interglacial periods (around 280-300 ppm)

pre-industrial times (around 280-300 ppm)

today (over 400 ppm)

How does the ocean play a role in controlling CO2 in the atmosphere?

The ocean acts as a massive carbon sink, absorbing large amounts of CO2 from the atmosphere through physical and biological processes

CO2 dissolves in seawater, forming carbonic acid, which is then utilized by marine organisms for photosynthesis or reacts with carbonate ions to form bicarbonate ions

Deep ocean currents store dissolved CO2 for extended periods, regulating atmospheric CO2 levels and playing a crucial role in the global carbon cycle

What is the biological pump, how does that play a role in the carbon cycle?

The process by which marine organisms transfer carbon from the surface ocean to the deep ocean

Role in carbon cycle

Photosynthesis

Phytoplankton in sunlit surface waters use CO2 and sunlight to create organic matter

Food chain + sinking

Zooplankton eat the phytoplankton, and larger organisms eat the zooplankton. Some of this organic matter (in the form of dead organisms, fecal pellets, etc.) sinks to the deep ocean

Sequestration

The carbon in the sunken material is removed from the surface system for long periods, helping regulate atmospheric CO2 levels

What is the “iron hypothesis”? Be able to explain the feedback process behind this idea—were ice ages more or less dusty, more or less ocean productivity, more or less CO2 in the atmosphere?

Processes that iron limitation in certain ocean regions restricts phytoplankton growth. Thus, adding iron could stimulate blooms, increasing carbon dioxide (CO2) uptake from the atmosphere

Feedback process

Ice ages were dustier

Colder, drier climate led to more exposed land, increasing wind-blown dust transport, including iron-rich particles, to the ocean

More ocean productivity

Increased iron supply fertilized phytoplankton growth, enhancing the biological pump

Less Atmospheric CO2

More carbon was drawn from the atmosphere into the ocean and eventually sequestered in the deep sea, contributing to lower atmospheric CO2 levels during glacial periods

Why do human emissions of CO2 matter?

Disrupting the carbon cycle

We’re adding CO2 to the atmosphere much faster than natural processes can remove it, overloading the system that normally regulate carbon levels.

Accelerating climate change

CO2 is a potent greenhouse gas. Excess CO2 traps heat, leading to global warming, rising sea levels, more extreme weather events, and a cascade of environmental consequences

What is ocean acidification? What impact does it have on the ocean?

The decrease in ocean pH due to the absorption of excess carbon dioxide from the atmosphere

The ocean becomes more acidic, although technically it still remains alkaline

Impact on ocean

Makes it harder for organisms like corals, shellfish, and some plankton to build their calcium carbonate shells and skeletons

Can disrupt marine foods webs, harm ecosystems, and impact industries like fishing and aquaculture

What chemicals regulate the pH of the oceans (CO2 and CaCO3)?

Carbon dioxide

When CO2 dissolves in seawater, it forms carbonic acid (H2CO3), which releases hydrogen ions (H+), lowering the pH (making the ocean more acidic)

Calcium carbonate

CaCO3 acts as a buffer. It can react with excess hydrogen ions (H+) to form bicarbonate (HCO3-), which helps resist changes in pH and maintain a more stable ocean environment

How does ocean acidification affect marine life?

Calcification challenges

Makes it harder for organisms like corals, shellfish, and some plankton to build their calcium carbonate shells and skeletons. This can lead to weaker structures, reduced growth rates, and increased vulnerability

Physiological impacts

Acidic conditions can disrupt physiological processes in some marine animals, affecting metabolism, reproduction, and overall health

How is the pH of the ocean expected to change as earth’s temperature and CO2 in the atmosphere increase?

pH will decrease

as atmospheric CO2 increases, more of it dissolves into the ocean, leading to a decrease in ocean pH (i.e., becoming more acidic)

Warmer waters hold less CO2

Increased temperatures reduce the ocean’s ability to absorb CO2, further exacerbating the acidification process

About how much might sea level rise by 2100 (very approximately—none? A little (1-2ft)? a significant amount (10 ft or more)? A whole lot (100 ft or more)?

Likely range

1-3 feet (30-90 cm) is the most probable scenario based on current scientific understanding

High-end scenario

Up to 7 feet (around 2 meters) is possible if we have rapid ice sheet melt and continue with high greenhouse gas emissions

(It’s very unlikely to see 100 feet of sea level rise by 2100. That scale of change would require a complete collapse of major ice sheets and takes centuries to millennia)

What are some strategies people have to adapt to or mitigate sea level rise? Know both natural and man-made erosion reduction tools.

Adaptation strategies

Managed retreat

Relocating structures and infrastructure away from the coastline

Accommodation

Raising buildings on stilts, designing flood-able landscapes, and improving stormwater management

Erosion reduction tools

Natural

Beach nourishment: Adding sand to widen beaches and provide buffer

Living shorelines: Using vegetation (marshes, mangroves) to stabilize shorelines and absorb wave energy

Man-made

Seawalls: Hard structures built parallel to the shore to block waves and erosion

Groins and jetties: Structures built perpendicular to the shore to trap sand and reduce erosion in specific areas (but can worsen it elsewhere

How do mangroves and marshes reduce erosion?

Dampen wave energy: Their dense root systems and tangled above-ground structures absorb wave energy, reducing the erosive force on the shoreline

Trap sediment: They act as natural filters trapping sediment carried by rivers and runoff. This helps build up the coastline and provide a buffer against erosion

What are the causes of modern sea level rise? Know climate related and climate independent causes. Which cause is responsible for the largest proportion of SLR?

Climate related causes (contributing the vast majority of sea level rise)

Thermal expansion

As the ocean warms, it expands, taking more volume. This is currently the largest contributor to sea level rise

Melting glaciers and ice sheets

Warming temperatures are causing glaciers and ice sheets to melt, adding water to the oceans

Climate-independent causes (relatively minor contribution)

Land subsidence: Sinking of some coastal landmasses due to natural processes (e.g., sediment compact) or human activities (e.g., groundwater extraction)

Largest contributor

Thermal expansion and glacial melt from climate change are the biggest factors driving modern sea level rise

Know something about ice cores and the types of information that can be extracted from them.

Past atmospheric conditions

Trapped air bubbles contain ancient gas samples, revealing past levels of carbon dioxide (CO2), methane, and other greenhouse gases

Isotopic rations (e.g., of oxygen) in the ice itself help scientists reconstruct past temperatures

Environmental records

Dust and ash particles provide clues about volcanic activity and wind patterns

Pollen helps identify past vegetation types, indicating shifts in plant communities over time

What controls atmospheric CO2 levels on long timescales (i.e., tens of millions of years and longer)? What are the sources and sink of CO2?

Controls

Tectonic processes: Plate tectonics influences volcanism (which releases CO2) and continental weathering rates (which removes CO2)

Weathering-climate feedback: Warmer climates increase weathering, which removes CO2; cooler climates slow weathering, allowing CO2 to build up

Sources of CO2

Volcanic outgassing: Releases CO2 stored in the earth’s mantle

Sinks of CO2

Silicate rock weathering: Chemical breakdown of rocks removes CO2 from the atmosphere, eventually forming carbonate sediments on the ocean floor

Organic carbon burial

Burial of dead plants and algae that haven’t decomposed, locking away their carbon

What do we mean by the tectonic/weathering climate thermostat? How might negative feedbacks work to help regulate CO2 levels?

The link

Techtonic activity like sea floor spreading and mountain building influences volcanic outgassing (a source of CO2) and the rate of rock weathering (a sink for CO2)

Negative feedback

This system acts as a negative feedback loop. When atmospheric CO2 levels rise, weathering rates generally increase. This is because warmer temperatures associated with higher CO2 can accelerate chemical breakdown of rocks, removing CO2 from the atmosphere. This acts a natural mechanism to bring atmospheric CO2 levels back down

Slow process

However, this feedback loop operates over geological timescales (millions of years). It’s important to note that this natural thermostat is too slow to keep pace with the rapid increase in CO2 emissions from human activities in recent centuries

What is meant by the Faint Early Sun Paradox? What’s the paradox and what’s the explanation for it?

The paradox

Early earth, billions of years ago, had liquid water on its surface despite the sun being fainter (less luminous) than it is today. This seems contradictory because a fainter Sun would be expected to provide less heat, potentially causing the earth to freeze

Explanation

Several factors likely contribute to warming earth’s surface for liquid water

Greenhouse gases: Higher concentrations of greenhouse gases like methane and carbon dioxide in the early atmosphere trapped more heat from the sun, keeping temperatures above freezing

Different atmospheric composition: The early atmosphere may have had a different composition compared to today, with less oxygen and more methane, which is a more potent greenhouse gas

Uncertainties

The exact reasons for earth’s early warmth are still being researched. The role of factors like cloud cover and variations in solar activity during the early sun’s evolution are also being explored

Why has the Sun become more luminous over time?

Nuclear fusion

The sun generates energy by fusing hydrogen atoms into helium in its core

Increasing core density

As this fusion process occurs, the ore of the sun becomes denser and hotter. This increases the rate of fusion reactions, leading to a gradual increase in the sun’s energy output