GEO011 Midterm 2

Climate Sensitivity

Amount of warming that we expects to occur when there is a change in the factors that control climate (e.g., increase in GHGs)

Best estimate of climate sensitivity

3.0 C (5.4 F)

According to IPCC AR5, what is the range of climate sensitivity?

1.5 to 4.5 C

Where do estimates of climate sensitivity come from?

1. Climate Models

2. Deep ocean temperature

3. Climate Proxy Data (tree rings, ice cores, etc.),

4. Clues from Deeper Time (Paleoclimatic Data)

What causes the delay in warming in response to a doubling of CO2?

Equilibrium Climate Sensitivity takes into account that it is due to delayed ocean warming.

Why are future projections of climate change uncertain? Or more specifically, what are the two main sources of uncertainty?

1. Unknown trajectory of future GHG emissions.

2. Uncertain response of the climate to these emissions

How can scientists draw certain conclusions?

1. Best-guess scenarios of fossil fuel burning

2. Average projections of climate models

How are sunspots related to solar intensity? In modern climate, are there more sunspots (a brighter sun) than those (that) in the Little Ice Age?

1. Sunspot records are available from the early 17th century through today.

2. More (less) sunspots = brighter (dimmer) sun

How was the Last Glacial Maximum (LGM) different than today? Why is the LGM cooler than today?

How were atmospheric concentrations of greenhouse gases (GHGs) different?

CO2 content ~50% of what it is today (~180 ppm).

Methane (Nitrous Oxide) was about ⅕ (⅔) of what it is today.

How are Sea levels different in the LGM than today

During the last ice age, sea level was 120 m (395 ft) lower.

How are Ice Sheets in LGM different than today?

Vast ice sheets covered much of Canada, northernmost US, Scandinavia, and Europe. About half of the cooling is due to the corresponding increase in reflectivit

How is Earth’s orbital configuration in LGM different than today?

Earth’s orbital configuration was also different > summer sunlight at high northern latitudes was reduced > winter snow could survive the summer > additional ice accumulated.

How has CO2 varied over geologic time scales? Has it varied a lot, or a little?

1. CO2 levels were high 500 mya, then fell, reaching a minimum 300 mya at the height of the Permo-Carboniferous glaciations on Gondwana.

2. After levels rose and fell, reaching another maximum 175 mya in the late Triassic.

3. Stayed relatively high through the next 100 mya (age of the dinosaurs > reptiles lived in the Arctic)

4. Since then CO2 has fallen, reaching another minimum close to present day.

5. Combined with paleo-temperature data, proxy CO2 data provide a climate sensitivity of 2-5 C (4-9 F) for each doubling of CO2.

What do fossil-fuel emissions scenarios consider? 

Driving forces of consumption are highly complex involving population growth and per-capita energy demand.

• These factors are in turn closely linked to economic growth and technological advances that accelerate consumption and shift it to other climate-neutral sources.

How are Representative Concentration Pathways (RCPs) defined?

From the 5th assessment by the IPCC defines four scenarios based on their “total radiative forcing” by 2100: RCP 2.5, RCP 4.5, RCP 6. And RCP 8.5. 

What is meant by a “business-as-usual” scenario?

Business-as-usual scenarios > Increasing fossil fuel use (RCP8.5)

Business-as-usual

RCP8.5

A conservation/mitigation scenario?

Conservation/mitigation scenarios > Future reduction of fossil fuel use (RCP2.6)

Conservation/mitigation scenarios

RCP2.6

What is the “faux pause”?

Temperatures haven’t increased as rapidly over the past decade as they did in the prior few decades has led to the false notion that there is a “pause” in global warming.

Can “faux pause” be simulated by models?

Not simulated by most model simulations.

What caused “faux pause”?

1. Background volcanic activity,

2. Short-term reduction in solar output

3. Series of La Niña events, all of which have led to temporary surface cooling not taken into account in most simulations.

Is it truly indicative of a pause in global warming?

Not a pause. 

The increasing heat content of the oceans, and the accelerating loss of Arctic sea ice, climate change and global warming are unfolding on, or ahead of, schedule.

How well did past IPCC projections do?

Quite Well

1. Actual CO2 increases since 1990 (FAR) have tracked roughly in the center of the projected range. 

2. Although the globe has warmed up a bit less than model projections (due to natural factors), projected warming is consistent w/ observations.

3. Sea level rise projections have fallen in each successive IPCC assessment.

4. Projections are consistent with the observed acceleration (as more land ice melts).

5. Substantial melting of ice sheets has begun earlier than expected upper end of projected range has been revised upward in AR5.

Does IPCC overstate the effects of climate change?

1. Opposite appease to be true

2. Decreasing trend of Arctic sea ice > observes decline is larger than model projections.

Under RCP8.5, how much warming does IPCC project by 2100?

Warming is 2.5-4.6°C (4.5-8.3°F) from 2000-2100

• Or 3.8-6.8°C (6.8-12.2°F) relative to preindustrial times for the least conservative, business-as-usual scenario.

Under RCP2.6, how much warming does IPCC project by 2100?

Warming of 0.2-1.8°C (0.4-3.2°F) from 2000-2100

• Or 1.2-2.8°C (2.2-5.0°F) relative to preindustrial times for the most conservative scenario.

Is the surface warming spatially uniform?

No

What are the warming patterns and reasons?

• Greatest warming over polar latitudes in Northern Hemisphere (NH) due to positive feedbacks of melting ice.

• Greater warming over land than ocean due to the fact that water tends to warm more slowly > Greater NH warming (more land)

• Weak North Atlantic warming due to change in ocean currents (weakening of Thermohaline Circulation)

Which continent will see the most warming?

North America

How is precipitation projected to change? Why?

Projected poleward shift of jet stream may cause: Increased winter precipitation in polar and subpolar regions; decreased summer precipitation in many mid-latitude regions.

Poleward expansion of the Hadley cell will cause decreased precipitation in subtropics.

Warmer atmosphere will cause increased precipitation near the equator. 

How are floods and droughts projected to change? Why?

Decrease summer precipitation + increased evaporation due to warming surface temperature > greater tendency for drought in many regions.

More evaporation, more precipitation > more vigorous cycling of water through atmosphere > more frequent, intense rainfall events and flooding for many regions. 

What is El Nino Southern Oscillation (ENSO)?

A natural irregular oscillation of the climate system, involving inter-related changes in sea surface temperatures (SSTs), currents, and winds across the tropical Pacific.

How does the tropical Pacific change during El Nino?

Descending air and high pressure brings warm, dry weather.

Weakend Southeast trade winds

Warm weather flows eastward, accumulating off South America.

Reduced or absent Cold upwelling due to weakened trade winds.

Low pressure and rising warm, moist air associated with heavy rainfall.

How does the tropical Pacific change during La Nina?

Low-pressure system, positioned farther west than normal.

Pool of warm water positioned father west than normal.

Stronger Southeastern trade winds than usual.

Strong upwelling of cold, deep water.

Cooler sea surface than normal in eastern Pacific

How long will it alternate between El Nino and La Nina?

This phenomenon alternates every few years (2-7 years, average 4 years)

How will El Nino affect global patterns of temperature and precipitation?

1. Weakening/reversal of southeast trade winds

2. Warmer water in the eastern tropical Pacific

3. Reduction in cold upwelling off coast of South America

4. Wetter conditions in southern United States

What are the characteristics of ENSO projections (climate overall? ENSO magnitude?)

Most (but not all) model predict a more El Nino like pattern (x-axis); Equal chance of increase/decrease in ENSO magnitude (y-axis)

Are ENSO projections certain?

Hampered by uncertainties in how some global winds and ocean currents will change, most notably ENSO.

What is a hysteresis loop? Tipping points? 

Some environmental systems operate on a hysteresis loop, in which they are two stable states

How are they related to “abrupt climate change”?

If the climate warms too much (i.e, past a threshold) ice sheet melting will become unstoppable.

Case of Ice Sheets

Only way to restore ice sheet is for temperatures to drop

What are the main reservoirs of carbon and processes of carbon transfer in the carbon cycle?

Atmosphere, Ocean, and Vegetation, Soils, and Detritus on Land

Is photosynthesis important? Respiration?

Various processes transfer carbon between these reservoirs, including photosynthesis, respiration, ocean–atmosphere gas exchange, and ocean mixing.

Does all of our CO2 emission stay in the atmosphere? If not, where does it go?

55% of the CO2 has “disappeared” > some dissolved into the ocean, the rest is incorporated into living biomass via photosynthesis.

Land Biosphere Carbon Cycle (Positive Feedback)

A warmer land leads to increased growth and respiration (CO2 byproduct) of soil microorganisms > carbon in soils is now being converted to CO2 at increasing rates. 

Land Biosphere Carbon Cycle (Negative Feedback)

Plants increase their growth in response to elevated CO2 (“CO2 Fertilization”).

Ocean Carbon Cycle (Positive Feedback)

A warmer ocean has less ability to absorb atmospheric CO2

Ocean Carbon Cycle (Negative feedback)

Ocean acidification reduces the production of calcium carbonate (CaCO3; limestone) by organisms (corals, plankton).

1. When these organisms grow their CaCO3 skeletons (i.e., to calcify), CO2 is released to the water. So calcification reduces the ocean’s ability to take up fossil-fuel CO2. 

2. Thereby, less calcification will increase the ocean's ability to absorb atmospheric CO2. 

Biological Pump Feedback (Positive)

CaCO3 is relatively dense & acts as a ballast once as an organism dies, carrying its tissues to deep ocean > this “pump” of carbon removes CO2 from surface waters, allowing more CO2 to be absorbed.

• Loss of the ballast reduces the ocean’s ability to take up atmospheric CO2.

Biological Pump Feedback (Sluggish Ocean) (Positive)

Slowing of ocean circulation reduces the mixing of nutrients:

• Slows biological productivity

• Weakens biological pump > reduces ocean’s ability to absorb CO2.

Rock Weathering (Negative Feedback)

Increased temperature and rainfall stimulate chemical weathering of rocks (the process that turns rock into soil and into dissolved salts in rivers). 

1. Atmospheric carbon dioxide dissolved in rain forms carbonic acid, which aids the rock-weathering process during which CO2 is converted to other forms of dissolved carbon. 

2. Increased weathering (during warming), therefore, removes CO2 from the atmosphere.

Which type of feedback dominates?

Positive feedbacks prevail > Warming is reducing nature’s ability to absorb atmospheric CO2.

What does this imply for future climate change?

Models that simulate both the carbon cycle and climate have been run with some, but not all, of these feedbacks.

1. Overall effect of these carbon cycle feedbacks is a more rapid buildup of atmospheric CO2, and a warmer climate. 

How is sea level projected to change by 2100? Why?

Sea level predicted to rise 0.5-1.2 m (1.6-3.9 ft) by 2100 for two reasons:

1. Water becomes less dense (expands) as it warms. A small rise of 0.1–0.4 m (0.3–1.3 ft) is predicted by 2100 due to this effect alone.

2. Melting of continental ice (not sea ice) including mountain glaciers and permanent ice caps. Melting of glaciers and ice caps > adds ~0.5 m (1.6 ft) of sea level rise.

How much will sea level rise with an eventual melting of Greenland?

5–7 m (16–23 ft)

How much will sea level rise with an eventual melting of West Antarctic?

5 m (16 ft)

What are some of the uncertainties associated with IPCC projections of future sea level rise (e.g., crevices/moulins)?

Crevices (“moulins”) > Crack/fissure in ice sheet > Meltwater to penetrate deep into the ice sheet and lubricate the base, allowing large pieces of ice to slide quickly into the ocean.

1. Could lead to a far more rapid disintegration of ice sheets than predicted by any current models. 

Will sea level rise happen everywhere over the globe (note the rebound effect)?

Sea-level has risen, except in regions (eastern Canada) where rising of the coastline has occurred due to Earth’s slow rebound from the ice age. 

How does sea level rise affect land and Gross Domestic Product (GDP)?

Even with 1 m of sea level rise—which could occur by the end of this century—losses of land and GDP are sizeable.

1. Losses rise dramatically at 5 and 10 m melting of Greenland would ensure the former; melting of West Antarctic ice sheet would ensure the latter.

How is extreme weather projected to change?

Likely that the frequency and intensity of extreme weather events will change.  

1. For certain extreme weather events, such as severe frosts and extended heat waves, the science is fairly definitive and the predicted changes are intuitive. 

2. More warming, more pronounced these trends will be. 

3. Changes vary regionally.

Severe frosts?

As temperatures warm, the probability of frosts (nights when temperatures dip below freezing) will decrease markedly.

1. Greatest decrease in interior North America and Asia, where winter temperatures have been traditionally the coldest.

Heat Waves?

Are likely to become more intense, more frequent, and longer lasting.

1. Greatest increase is predicted in western U.S., North Africa, and the Middle East, where feedback loops associated with decreased soil moisture may intensify summer warmth.

Intense rainfall events and flooding?

Increases in the frequency of intense precipitation events and corresponding flooding are expected.

1. Due to more vigorous water cycle that will accompany a warmer climate, with greater amounts of moisture in a warmer atmosphere 

Dry Spells

While many regions are likely to become drier, scientists predict that even in those regions individual rainfall or snowfall events

Will become more intense, although longer dry spells will separate them. 

Hurricanes

• More intense hurricanes in certain ocean basins, such as the tropical Atlantic basin, and that these trends closely mirror warming ocean surface temperatures

  • Warmer SSTs, all other things being equal, is likely to fuel more intense tropical cyclones, with stronger sustained winds. 

  • Combination of sea level rise and stronger tropical storms could pose a “double whammy” when it comes to damaging storm surges. 

  • Model simulations indicate a likely shift toward the strongest (Category 4 and 5) tropical cyclones over the next century, given projected climate changes.

What are required to achieve lower stabilization targets?

All stabilization targets require sharp reduction in CO₂ emissions following the peak. 

• Low stabilization levels require CO₂ emission rates to fall below the current rate within a few decades.

To stabilize CO2 level at 450, 550, 750 ppm, by which year we need to reach emission peak?

450 ppm : 2020

550 ppm : 2040

750 ppm : 2080

Under climate change, what are the threats to coastal and low-lying regions (e.g., Bangladesh, Southern Florida, Netherlands)?

• Rising sea level

• Increasing tropical cyclone destruction

• Increasing coastal erosion

• Larger wave heights all pose serious threats to coastal and low-lying regions.

With 6 meters of sea level rise, will most of New York City be submerged?

Most of New York City and Boston would be submerged if sea level were to rise by 6 m (19.6 ft).

What will be human loss in the coastal regions that are even not inundated by higher sea level?

1. increased exposure to flood and storm damage

2. more intense coastal surges

3. altered patterns of coastal erosion

How does global warming affect air pollution? Why?

1. Smog is produced when emissions from incomplete fossil-fuel combustion react to produce pollutants.

2. One such pollutant is tropospheric ozone, a lung irritant that also damages crops, buildings & forests.

3. Warming accelerates ozone production & promotes air stagnation, leading to increased tropospheric ozone levels.

4. One model indicates that for every 1°C increase in global temperature, there will be 20,000 additional pollution related deaths.

What is an ecosystem?

An interdependent community of plants, animals, and microscopic organisms, and their complex physical environment.

List ecosystem boundaries delineated by climate.

1. Desert ecosystems in the subtropics

2. Tropical rain forest ecosystems near the equator

3. Tundra ecosystems near the poles

Why are ecosystems valuable?

They assist us with:

1. Provisions

   1. Food (seeds, fruits, game, spices);

   2. fiber (wood, textiles);

   3. medicinal and cosmetic

   4. products (dyes, scents)

2. Environmental Regulation

   1. Climate and water regulation,

   2. water and air purification,

   3. carbon sequestration,

   4. protection from natural disasters, disease, and pests.

3. Cultural Benefits

   1. Appreciation of, and interaction with, the natural world

   2. recreational activities.

How does climate change affect ecosystems? Biodiversity?

1. As climates have changed in the geologic past, ecosystems have shifted in response.

2. But past climate changes were slower than the projected future changes human activity is already pushing ecosystem resilience, and may lead to species extinction if they cannot adapt or migrate fast enough.

According to the IPCC, what is the most vulnerable ecosystem? Why?

“Coral reefs are the most vulnerable marine ecosystem with little scope for adaptation”. 

“Coral Bleaching”?

Loss of algae that live in a symbiotic relationship with the coral & give it color —is linked to exceptionally hot ocean temperatures.  Human induced global warming will contribute to this.

Why coral reefs and wetlands are important?

Most diverse ecosystems

Provide:

1. Food for hundreds of millions of people

2. A defense barrier against tropical cyclones and tsunamis

3. Source of tourism income 11.5B annually 

Why wetlands are important?

Provide an important service to their surroundings.

Sediment contamination—including iron and acidity from mine runoff, and nitrogen from farm fertilizers—are removed as water percolates through wetlands before entering our drinking and irrigation water.

1. Are biologically diverse, providing homes for endangered species and a refuge for migrating birds.

2. Ideal places for recreation

Besides coral, what other animal species will be at particular risk of extinction under continued climate change?

1. The precarious future of the polar bear depends on expansive sea-ice cover to reach and feed on seals.

2. Birds, reptiles and amphibians have all been affected.

As climate has changed in the geologic past, ecosystems (plants, animals, microscopic organisms, etc.) have shifted in response. How is past climate change different than projected future changes?

Past climate changes were slower than the projected future changes human activity is already pushing ecosystem resilience, and may lead to species extinction if they cannot adapt or migrate fast enough. 

How is this related to migration rates?

1. Climate change exceeds the natural migration capacities of most plants and animals for the higher-emission scenarios.

2. Climate zone migration is faster across flat areas  (less mountains).

What does this imply for ecosystems, biodiversity and individual species? Or more specifically, under 2oC and 4 oC warming, what percentage of plant and animal species will be at risk of extinction, respectively?

1. AR4 (AR5) reported with medium (high) confidence that 20-30% of plants and animals will be subject to increased risk of extinction if global temperature rise to 2.0°C above pre-industrial.

2. 40-70% at risk with a temperature rise of 4.0°C.

3. Extinction is irreversible.

What are MPAs?

Restrict human activity for a conservation purpose, typically to protect natural or cultural resources 

Are MPAs effective at reducing fish and coral loss?

Have proven effective at staving off coral and fish losses, and are of great economic benefit.

Can MPA they protect coral from global warming? Ocean acidification? If not, then what needs to be done?

They cannot protect coral from global warming, nor can they protect from acidification effects of CO₂ recall, ocean and land biosphere have absorbed about 50% of our CO₂ emissions. 

1. When CO₂ dissolves into ocean water, it is transformed into carbonic acid makes water less conducive to coral growth.

2. If fossil fuel burning rates continue to increase, corals will be unable to grow skeletons by the end of this century.

3. Only way to prevent this catastrophe is to reduce or eliminate CO₂ emissions, or to sequester it before it escapes into the atmosphere.

How does climate change stress human societies [e.g., natural resources, fresh water supplies, water pollution, food supplies, human health?

Climate change puts stress on human societies.

It will likely lead to greater competition for natural resources, threats to food supplies, increased risks to human health, and international conflict.

Diminished or unreliable fresh water supplies. 

Combination of warmer water, more intense rainfall events, and longer periods of low river levels and stream flows will also exacerbate water pollution.

What will happen when nations exceed their capacity to adapt to climate change?

Violence and destabilization could ensue, leading to unprecedented levels of conflict both between, and within, nations.

How might climate change affect environmental refuges? Why?

Expanded patterns of drought and conditions unfavorable for agriculture/farming likely to change what constitutes desirable land.

1. Sea level rise and other factors will likely make currently inhabited regions inhospitable to humans > increasing competition for habitable land.

With modest warming, how will food production change? With more warming (>3oC)?

Climate change could undermine food supplies.

1. Many of the regions most affected already find it difficult to meet existing food demands.

2. Generally: Short-term positives, long-term negatives.

Is food production dependent on regions with more warming?

Some regions (US, Europe, Canada) stand to benefit with moderate warming (1-3°C), due to increased crop and livestock productivity.

How will food production be affected with modest warming?

Food production expected to increase with modest warming (1-2°C).

Effect of socioeconomic development on food supply with modest warming

Could partially, or completely offset, the negative impacts on food supply.

Projections for the number of undernourished people by 2080 range from a reduction to 100M to an increase to 1.3B (currently 820M).

How will climate change affect disease (Malaria, dengue, West Nile Virus)? Why?

1. Disease can spread as climate changes—insects and rodents that carry disease range more widely as climate barriers are lifted.

2. Evidence that vectors such as ticks are spreading to higher latitudes and altitudes in Canada and Sweden.

3. Ragweed = more pollen over a longer season.

4. Malaria could also expand.

How is climate change related to mosquitos and other vectors?

Disease carrying mosquitos typically confined to warmer climates are spreading into the extratropics, carrying infectious diseases like dengue and West Nile virus.

Are the health impacts associated with climate change uniformly distributed across the globe?

Climate change related health impacts will not be uniformly distributed across the world’s population.

Who is more susceptible to health impacts associated with climate change distributed across the globe?

1. Poor nations will be more susceptible inadequate access to air conditioning, infrastructure (clean water, supplies, electricity), health care & emergency response facilities.

2. In all countries, children, elderly, & urban poor will suffer disproportionately, as well as those living in low-lying coastal areas.

How large are rates of Arctic and land masses in Arctic of warming? (3.p60)

1. Over last ~50 years, Arctic Ocean’s summertime sea-ice minimum has decreased at 9-14% per decade exposes darker ocean, resulting in more warming.

2. Snow free period has increased by 5-6 days every decade exposes dark ground that absorbs more sunlight more warming.

3. Arctic is warming at twice the rate of the globe; landmasses in Arctic are warming at 5x.

4. Rate of loss of Greenland and West Antarctic ice sheets has increased markedly over last two decades.

What are the projected change of Arctic sea ice?

1. Models project the Arctic Ocean will be ice-free in September later this century under RCP8.5.

2. Smallest projected change is 43% decline in year-around sea ice cover for RCP2.6