EVR1001 Midterm 1 Short Answer Questions

1) How certain are scientists that humans are causing global climate change? Describe the language used by scientists and some of the particular climate trends they have identified as changing. If the scientific community is convinced of the evidence, why is there still debate?

Scientists believe that global climate change caused by humans is equivocal or extremely likely. Some of the trends include rising global average temperatures, melting glaciers, rising sea levels, and ocean acidification. There’s still a debate, because of economic and political interests in relation to fossil fuels.

2) Please list three facts about climate change that the scientific community agrees on completely and two things that are still being debated by some climate scientists. For the two that are still being debated, please state what most scientists believe.

Three facts completely agreed on is the rising of global temperatures, atmospheric carbon dioxide levels increasing due to human activities, and increased greenhouse gases in the atmosphere is trapping in heat. Two things that are still debated are how much warming results from doubled carbon dioxide, most scientists believe it falls between 2.5-4 degrees Celsius. Also, with how specific regions will be affected, most scientists believe effects, such as rising sea levels and extreme weather will occur.

3) Describe the demographic transition and illustrate how the transition takes place with a figure? Describe different types of age structures observed in countries around the world and how these age structure impact current and future environmental conditions?

The demographic transition shows how birth and death rates change as a country develops economically, usually in 4 stages. There’s 3 age structures: Expanding, stable, and contracting. Expanding structure occurs when younger individuals make up majority of the population, which would lead to greater population growth, increased demand for resources, and greater environmental pressure. Stable structure occurs when there’s an even distribution of ages, with population and resource demand remaining steady. Contracting structure occurs when older individuals make up majority of the population, which would leader to slower population growth, with a decreased strain on population and could lessen environmental problems.

4) Is extinction natural? How has extinction rate changed over time? Why are extinction rates today different than in the past?

Yes, extinction is natural. The extinction rate hasn’t been constant, and has changed over time due to mass, rapid wipeouts of species, followed by long periods of recovery and diversification. Extinction rates are different today than in the past, because of human caused drivers as opposed to a natural event, such as habitat destruction, climate change, pollution, and invasive species.

5) In the food web depicted on the right, what is the trophic level of the bear when feeding on berries? What is the trophic level when feeding on deer? How would you expect the population of bears to vary if it fed only on berries or only on deer? Name two species that are competitors.

The bear’s trophic level would be a primary consumer when eating berries, and secondary consumer when feeding on deer. I expect the bear population to vary if it only consumed berries, that they would be able to consume more energy due to no deer taking away energy through the 10% rule from the berries and could sustain a bigger bear population. In comparison, I expect the bear population to differ if it only consumed deer by receiving less energy due to energy being lost each trophic level. Two species that are competitors are the red-tailed hawk and grizzly bear.

6) How have humans altered the phosphorus and nitrogen cycles? Please explain an important way in which phosphorus and nitrogen cycles differ.

Humans have altered the Nitrogen cycle by the use of fertilizers, fossil fuel combustion, and Nitrogen fixing crops like legumes. The Phosphorus cycle has been altered by fertilizer use, detergents, and agricultural runoff. Comparing both, Nitrogen has a greater atmospheric component compared to Phosphorus. Nitrogen gas makes up most of the atmosphere and the cycle includes processes like fixation, nitrification, and denitrification that move nitrogen between atmosphere and biosphere. Phosphorus primarily moves through weathering, soil, and water without a gaseous phase, making it a slower cycle compared to Nitrogen.

7) What are Milankovitch Cycles? How are they caused? Why are they important?

Milankovitch Cycles are periodic variations in Earth’s orbit and axial orientation which affect the distribution of solar radiation reaching Earth. They’re caused by eccentricity, the shape of Earth’s orbit, obliquity, the tilt of Earth’s axis, and the precission, the movement of Earth’s rotational axis. These cycles are important because they change the distribution and intensity of sunlight received at different latitudes and seasons and cause glacier-interglacial cycles.

8) Please explain the processes that drive the thermohaline cycle and also explain the reason that the thermohaline cycle is important for the Earth’s climate.

The processes are differences in water density which is controlled by temperature and salinity. The colder, denser water sinks and flows along the ocean bottom, and warmer, less dense water flows in to replace it, creating a slow, continuous global circulation pattern. The thermohaline cycle is important for Earth’s climate, because it redistributes heat around the planet, from the equator towards the poles. It also contributes to carbon sequestration, as sinking water carries dissolved CO2 into the deep ocean. Disrupting the circulation can change climate patterns.

9) Please list both a positive and a negative feedback on climate change that is associated with increased evaporation of water from the oceans. Explain what makes each a positive or negative feedback on global temperature.

A positive feedback could be increased water vapor in the atmosphere. Water vapor is a greenhouse gas, so more water vapor traps more heat, which leads to further warming, causing more evaporation. A negative feedback could be cloud formation. Clouds increase Earth’s albedo, reflecting more incoming sunlight back out before warming Earth. This cooling effect counteracts warming.

10) Is a carrying capacity a fixed entity? Discuss the role of humans in regulating carrying capacity for the human species and in altering the carrying capacity for other species.

No, carrying capacity isn’t fixed. Humans have increased their carrying capacity through innovations such as agriculture, medicine, and energy which allowed the human population to exceed further than compared to natural resource limits. Humans have altered carrying capacity for other species in many ways, such as some negative effects like habitat destruction, pollution, climate change, and resource competition. Other positive effects include conservation efforts like protected habitats and captive breeding, which can increase carrying capacity.