Global Warming Exam 2

1. What is climate sensitivity?

Amount of warming that we expect to occur when there is a change in the factors that control climate (e.g. increase in GHGs), expressed in terms of how much surface warming will occur in response to a doubling of CO2 from pre industrial levels (280 ppm) 

1. What is the best estimate of climate sensitivity?

3.0 degrees C (5.4 degrees F)

1. What is the range of climate sensitivity according to IPCC AR5?

1.5 to 4.5 degrees C

1. Where do estimates of climate sensitivity come from?

Climate proxy data, sunspot records, etc.

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

Equilibrium climate sensitivity: full amount of warming in response to an increase in GHGs may not be realized for many decades, due to delayed ocean warming

1. Why are future projections of climate change uncertain?

They are uncertain because of the unknown trajectory of future GHG emissions and uncertain response of the climate to these emissions.

1. How can scientists draw certain conclusions about future climate?

Through best-guess scenarios of fossil fuel burning and average projections of climate models

1. How are sunspots related to solar intensity?

More sunspots equals a brighter sun, less sunspots equals a dimmer sun.

1. In modern climate, are there more sunspots than those in the Little Ice Age?

Yes there are more sunspots now.

1. How was the Last Glacial Maximum different from today? Why was it cooler than today? How were atmospheric concentrations of greenhouse gases different? Sea level? Ice sheets? Earth’s orbital configuration?

The Last glacial maximum was different because CO2 content was about 50% of what it is today and methane was about ⅕ of what it is today. Vast ice sheets covered much of canada, northernmost UC, Scandinavia and Europe. About  half of the cooling is due to the corresponding increase in reflectivity. Sea level was 120 meters lower. Earth’s orbital configuration was different; summer sunlight at high northern lats was reduced so winter snow could survive the summer and additional ice accumulated.

1. How has CO2 varied over geologic time scales; has it varied a lot, or a little?

CO2 levels were high 500 MYA then fell reaching a minimum 300 MYA. After that, levels rose and fell reaching another maximum 175 MYA and stayed relatively high through the next 100 MYA, since then CO2 has fallen reaching another minimum close to present day. It has varied a lot.

1. What do fossil-fuel emissions scenarios consider?

It considers human consumption of fossil fuels and land-use, so population growth and per-capita energy demand as well as economic growth and technological advances.

1. How are Representative Concentration Pathways defined?

They are defined based on their total “radiative forcing” by 2100

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

 increasing fossil fuel use based on our use of fossil fuels right now.

1. What is meant by a conservation/mitigation scenario?

Future reduction of fossil fuel use.

1. What is RCP8.5?

Business as usual scenarios

1. What is RCP2.6?

conservation/mitigation scenarios

1. What is the “faux pause” and can it be simulated by most model simulations? What caused it? Is it truly indicative of a pause in global warming?

Temps haven’t increased as rapidly over the past decade as they did in the prior few decades, leading to the “faux pause” notion in global warming. It’s not simulated by most model simulations. It’s caused by natural factors such as volcanic activity, short term reduction in solar output, and a series of la nina events. It is not truly indicative of a pause in global warming.

1. How well did past IPCC projections do, and do they overstate the effects of climate change?

Projected warming is consistent with observations. IPCC do not overstate the effects of climate change, in fact the opposite appears to be true.

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

2.5-4.6 degrees C from 2000-2100 or 3.8-6.8 degrees C relative to preindustrial times

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

0.2-1.8 degrees C from 2000-2100 or 1.2-2.8 degrees C relative to preindustrial times

1. Is the surface warming spatially uniform? What are the warming patterns and reasons?

No it is not spatially uniform. The Greatest warming over polar latitudes in NH due to positive feedbacks of melting ice, greater warming over land than ocean because water warms slowly, so greater NH warming (more land). Weak North Atlantic warming due to change in ocean currents.

1. Which continent will see the most warming?

North America

1. How is precipitation projected to change? Why?

Increases in the frequency of intense precipitation events and flooding are expected because of the more vigorous water cycle with more moisture held in a warmer atmosphere.

1. How are floods and droughts projected to change? Why?

Many regions are projected to become dryer, and the rain there will become more intense with longer dry spells between them. Floods will become more common.

1. What is El Nino Southern Oscillation (ENSO)?

It’s a natural irregular oscillation of the climate system, involving inter-related changes in sea surface temperatures, currents, and winds across the tropical Pacific.

1. How does the tropical Pacific change during El Nino?

Descending air and high pressure brings warm, dry weather. Southeast trade winds reverse or weaken. Warm water flows eastward, accumulating off South America. Cold upwelling reduced or absent due to weakened trade winds. Low pressure and rising warm, moist air associated with heavy rainfall. 

1. How does the tropical Pacific change during La Nina?

Low pressure system, positioned farther west than normal. Pool of warm water positioned farther west than normal. Southeast trade winds stronger than usual. Strong upwelling of cold, deep water. Sea surface cooler than normal in eastern Pacific.

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

Alternates every few years.

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

Wet and cool in the southern United States, Warm in northern North America, eastern South America, and South Asia. Dry in South Asia and northern South America. Dry and warm in southern Africa.

1. What are the characteristics of ENSO projects (climate overall? ENSO magnitude?)

Most models predict a more El-Nino like pattern, there is an equal chance of increase and decrease in ENSO magnitude.

1. Are ENSO projections certain?

No, because there are uncertainties in how some global winds and ocean currents will change.

1. What is a hysteresis loop?

When an environmental system has two stable states

1. What are tipping points?

When the environmental system passes into an unstable state, for example, the Antarctic ice shelf is having rapid disintegration.

1. How are hysteresis and tipping points related to abrupt climate change? (Be familiar with the case of ice sheets)

West Antarctica may have already passed the tipping point; the edge of ice sheet has retreated away from seafloor ridge that it had rested upon, so ice margin now floating in deep water, without the friction at its base, ice flow to ocean melting zone is accelerating.

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

Main reservoirs are the atmosphere, ocean, vegetation, soils and detritus on land. The processes that transfer carbon between these reservoirs include photosynthesis, respiration, ocean-atmosphere gas exchange and ocean mixing.

1. Is photosynthesis and respiration important?

Yes, they play a vital role in the carbon-cycle.

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

No, about 55% of the CO2 we’ve emitted into the atmosphere has mostly dissolved in the ocean with the rest incorporated into living biomass via photosynthesis. 

1. What are positive feedbacks associated with the carbon cycle?

Warming is reducing nature’s ability to absorb atmospheric CO2. A warmer land leads to increased growth and respiration (CO2 byproduct) of soil microorganisms; so now carbon in soils is now being converted to CO2 at increasing rates.

1. What are negative feedbacks associated with the carbon cycle?

Plants increase their growth in response to elevated CO2 (“Co2 Fertilization”)

1. Which type of feedback dominates?

Positive feedbacks

1. What does this imply for future climate change? (Be familiar with 7 types of carbon cycle feedbacks)

More rapid buildup of atmospheric CO2, and a warmer climate.

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

It’s predicted to rise between 0.5-1.2 m by 2100 because of two treasons: water becomes less dense (it expands) as it warms which leads to a small rise of 0.1-0.4 m by 2100 due to this effect alone; melting of continental ice (not sea ice) including mountain glaciers and permanent ice caps, adding about 0.5 m of sea level rise.

1. How much will sea level rise with an eventual melting of the Greenland/ West Antarctic ice sheet?

Melting of greenland ice sheet: 5-7 meters, and melting of west antarctic ice sheet: 5 meters.

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

Some newly observed effects that could significantly accelerate the rate of melting have caused uncertainties. These include crevices (moulins) that lead to cracks and fissures in the ice sheet, leading to meltwater penetrating deep into the ice sheet, lubricating the base,allowing large pieces of ice to slide quickly into the ocean. This could lead to farm more rapid disintegration of ice sheets than predicted by current models.

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

No, regions in eastern Canada haven't experienced sea-level rise. This is because of Earth’s slow rebound from the ice age leading to the rising of the coastline.

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

It causes sizable losses of land and GDP. 

1. How is extreme weather predicted to change? Severe frosts? Heat waves? Intense rainfall events and flooding? Dry spells? Hurricanes?

The more warming the more pronounced the frequency and intensity of extreme weather events will change. The probability of frosts will decrease, heat waves will become more intense, more frequent, and longer, intense rainfall and flooding will increase, dry spells will become longer, hurricanes become more powerful.

1. What is required to achieve lower stabilization targets?

It can be achieved only with lower peak emissions; then a sharp reduction in CO2 emissions following the peak.

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

450, 2020. 550, 2040. 750, 2080.

1. 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, and larger wave heights.

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

Yes, most of NYC and Boston would be submerged.

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

Increased exposure to flood and storm damage, more intense coastal surges, altered patterns of coastal erosion. These can result in loss of human life, damage to infrastructure, degraded water quality, decreased availability of freshwater, loss of coastal habitats, and significant population displacement.

1. How does global warming affect air pollution? Why?

Pollutants such as tropospheric ozone are produced from incomplete fossil-fuel combustion. Warming accelerates ozone production and promotes air stagnation, leading to increased tropospheric ozone levels.

1. What is an ecosystem? List ecosystem boundaries delineated by climate.

An ecosystem is an interdependent community of plants, animals, and microscopic organisms and their complex physical environment. Ecosystem boundaries are generally delineated by climate: desert ecosystems in the subtropics, tropical rain forest ecosystems near the equator, and tundra ecosystems near the poles.

1. Why are ecosystems valuable?

They assist us with provisions (food, fiber, etc), environmental regulation (climate/water regulation, water/air purification, carbon sequestration, protection from natural disasters, disease, and pests), and cultural benefits.

1. How does climate change affect ecosystems? And biodiversity?

Climate change leads to shifts in ecosystems, which may lead to species extinction if we cannot adapt or migrate fast enough.

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

Coral reefs are the most vulnerable ecosystem because there is little room for adaptation.

1. What is “coral bleaching?” 

The loss of algae that live in a symbiotic relationship with the coral and give it color. Coral bleaching is linked to exceptionally hot ocean temperatures.

1. Why are coral reefs and wetlands important?

Coral reefs provide food for hundreds of millions of people, a defense barrier against tropical cyclones and tsunamis, and tourism income. Wetlands provide an important service to their surroundings such as spreading storm waters across a broad area thus reducing its energy and flooding downstream; it also helps by filtering our water and has a lot of biological diversity.

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

Amphibians, birds, reptiles, polar bears.

1. As climate has changed in the geologic past, ecosystems have shifted in response. How is past climate change different from projected future changes?

Past climate changes were slower than the projected future changes. 

1. How is climate change related to migration rates?

The rate of climate change exceeds the natural migration capacities of most plants and animals.

1. What does climate change in relation to migration rates imply for ecosystems, biodiversity, and individual species?

This means that 20-30% of plants and animals will be subject to increased risk of extinction.

1. What are MPAs? Are they effective at reducing fish and coral loss? Can they protect coral from global warming? Ocean acidification? If not, then what needs to be done?

MPAs are Marine Protected Areas that restrict human activity for a conservation purpose. They have proven effective at staving off coral and fish losses, but they cannot protect coral from global warming or ocean acidification. The only way to do this is to reduce or eliminate CO2 emissions.

1. How does climate change stress human societies, fresh water supplies, water pollution, food supplies, human health?

Increased competition among nations for diminishing natural resources, diminished or unreliable fresh water supplies, exacerbated water pollution, undermined food supplies, and negative effects on human health such as pests, pollens, and the spread of diseases.

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

Violence and destabilization could ensue, leading to war.

1. How might climate change affect environmental refugees? Why?

Increase in environmental refugees, about 25 million already displaced. Climate change appears to be driving migrations from the dry Sahel to West Africa, and exodus from parts of India, China, Central and South America.

1. With modest warming, how will food production change? Is this dependent on the region? With more warming (>3 degrees C) how will food production be affected? Note the effect of socioeconomic development.

With modest warming food production is expected to increase (in regions such as Us, Europe, and Canada), but with more warming there will be negative impacts for crops in all major agricultural regions.

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

Disease carrying mosquitoes that like warmer climates are spreading into the extratropics carrying those diseases.

1. Are the health impacts associated with climate change uniformly distributed across the globe? Who is more susceptible? Why?

No, the impacts are unequal. Poor nations will be more susceptible because of their inadequate access to air conditioning, infrastructure, health care and emergency response facilities. 

1. How large are rates of Arctic and land masses in Arctic warming?

The Arctic is warming at twice the rate of the globe, and landmasses in the Arctic are warming at 5x.

1. What is the projected change of Arctic sea ice?

Under RCP8.5, the models project that the Arctic Ocean will be ice-free in September later this century. Under RCP2.6, the smallest projected change is a 43% decline in year around sea ice cover.

1. The impacts (polar bear, new northern coastlines for North American and Eurasian nations, new sea routes for international trade)?

North American and Eurasian nations will suddenly have new northern coastlines to defend, new sea routes connecting the north Pacific and north Atlantic Oceans will open up, and polar bears risk extinction.

1. What is permafrost? How is it expected to change in a warmer world?

Permafrost is permanently frozen soil. In a warmer world, it’s expected to melt.

1. What are the impacts of permafrost melting?

Bridge collapse, pipeline breakage, roadway degradation, contamination of surrounding environments, and increased warming from trapped methane being released into the atmosphere from the melted permafrost.