Ecology and sustainability · Sustainability and global change
Climate change
Without the greenhouse effect, the Earth's average temperature would be about $-18\,^\circ\text{C}$, a frozen planet uninhabitable for life as we know it. The problem is not that the greenhouse effect exists, but that human activities are intensifying it much faster than ecosystems can keep up with.
The natural greenhouse effect
The Moon orbits at the same distance from the Sun as the Earth but has no atmosphere, so its average temperature is about $-20\,^\circ\text{C}$, whereas that of our planet is around $+15\,^\circ\text{C}$ (about $59\,^\circ\text{F}$): what atmospheric mechanism retains heat and stops the Earth's surface from being a frozen desert?
Greenhouse gases
Not every gas in the air traps heat. Nitrogen and oxygen do not. The main greenhouse gases (GHGs) are carbon dioxide, methane and nitrous oxide, plus water vapor.
Gas
Main sources
Carbon dioxide ($\text{CO}_2$)
burning coal, oil and natural gas; deforestation
Methane ($\text{CH}_4$)
cattle ranching, landfills, natural gas leaks, rice fields
Nitrous oxide ($\text{N}_2\text{O}$)
fertilizer on farm fields, manure
Methane and nitrous oxide trap more heat per molecule than $\text{CO}_2$. But $\text{CO}_2$ is emitted in far larger amounts and stays in the air for centuries, so it contributes the most to current warming.
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Look at the greenhouse effect diagram. Explain what each numbered arrow (1, 2, and 3) represents, why the natural greenhouse effect is essential for life on Earth, and…
Look at the greenhouse effect diagram. Explain what each numbered arrow (1, 2, and 3) represents, why the natural greenhouse effect is essential for life on Earth, and what the human-caused alteration of it consists of.
Last January a freeze hit Houston and Marcus said, "So much for global warming!" Is one cold week enough to show the climate is not warming? Let's find out.
Why are heat waves getting worse? Temperatures on any day vary around an average. If the whole average shifts up by even $1$ or $2\,^\circ\text{C}$, the whole range shifts, so extreme hot days that were rare become common and last longer, while extreme cold days become rarer.
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Distinguish between weather and climate, and explain why a week of intense cold in winter does not contradict the global warming trend, drawing on the difference between…
Distinguish between weather and climate, and explain why a week of intense cold in winter does not contradict the global warming trend, drawing on the difference between an isolated data point and a long-term average.
Name two pieces of evidence of climate change observed in Spain (the retreat of the Pyrenean glaciers, earlier flowering, more frequent heat waves, rising sea level on…
Name two pieces of evidence of climate change observed in Spain (the retreat of the Pyrenean glaciers, earlier flowering, more frequent heat waves, rising sea level on the coast) and explain what each one consists of.
What is a heat wave and how is it defined meteorologically? Explain why, in a warmer climate, heat waves are expected to become more frequent, longer, and more intense…
What is a heat wave and how is it defined meteorologically? Explain why, in a warmer climate, heat waves are expected to become more frequent, longer, and more intense even if the average temperature only rises by one or two degrees.
Describe two consequences of climate change already observable in the ecosystems of the Iberian Peninsula and explain the physical or biological mechanism that produces…
Describe two consequences of climate change already observable in the ecosystems of the Iberian Peninsula and explain the physical or biological mechanism that produces them.
In the carbon cycle, plants and oceans take in $\text{CO}_2$ and respiration, decay and fires release it, roughly in balance. Humans added a new flow: carbon that was stored underground for millions of years as coal, oil and natural gas. Burning these fossil fuels (for cars, power plants and heating) and deforestation (cutting and burning forests, which removes trees that absorb $\text{CO}_2$) are the two human processes that add the most to the atmosphere.
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Relate the carbon cycle to the increase in atmospheric $\text{CO}2$ since the Industrial Revolution, naming the two human processes that contribute most to this increase.
Relate the carbon cycle to the increase in atmospheric $\text{CO}_2$ since the Industrial Revolution, naming the two human processes that contribute most to this increase.
The concentration of atmospheric $\text{CO}2$ has gone from around $280\ \text{ppm}$ in pre-industrial times to around $420\ \text{ppm}$ today. Calculate the percentage…
The concentration of atmospheric $\text{CO}_2$ has gone from around $280\ \text{ppm}$ in pre-industrial times to around $420\ \text{ppm}$ today. Calculate the percentage increase and discuss what would have happened to ecosystems if this increase had occurred over centuries instead of less than two.
Mountain snow works like a frozen reservoir. In the Rocky Mountains and Sierra Nevada, winter snow melts slowly in spring and summer and feeds rivers such as the Colorado. In a warmer climate, more precipitation falls as rain instead of snow and the snow melts earlier. So rivers carry more water in winter and spring (with flood risk) and less in summer, when cities and farms need it most.
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Explain what the albedo of a surface is, which surfaces on Earth have a high albedo and which have a low one, and why the melting of Arctic sea ice reduces the planet's…
Explain what the albedo of a surface is, which surfaces on Earth have a high albedo and which have a low one, and why the melting of Arctic sea ice reduces the planet's average albedo.
The average temperature of the Iberian Peninsula has already risen by more than $1.5\ \text{°C}$ since pre-industrial times. Explain what consequences this warming has…
The average temperature of the Iberian Peninsula has already risen by more than $1.5\ \text{°C}$ since pre-industrial times. Explain what consequences this warming has for the snow cover of Spanish mountains and how it changes the flow regime of the rivers that rise in them (more water in winter, less in summer).
Faced with the advance of the climate crisis, a city like Houston can choose to run fleets of electric buses to cut emissions, or to plant shade trees and build flood barriers: why does managing climate change require distinguishing between tackling the origin of the warming and preparing for its unavoidable consequences?
Carbon sinks and net zero
Carbon sequestration is the capture and long-term storage of carbon. Natural carbon sinks absorb more carbon than they release. Forests store it in wood for decades to centuries, soils in organic matter for decades to millennia, and oceans as dissolved $\text{CO}_2$ for centuries.
Net zero means the greenhouse gases we emit equal the amount removed by sinks (or technology), so the net addition to the atmosphere is zero. It does not mean emitting nothing: some emissions are hard to eliminate, and sinks cancel them out.
Scientists cannot predict a single future temperature because it depends on human choices. A climate scenario is a projection of how much warming results from a given path of emissions (energy use, economy, population). The IPCC compares low, medium and very high emissions scenarios, so the outcome is a range, not one number.
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Explain what carbon sequestration is and name two natural carbon sinks (forests, soils, oceans, peat bogs), indicating how they store carbon and for how long.
Explain what carbon sequestration is and name two natural carbon sinks (forests, soils, oceans, peat bogs), indicating how they store carbon and for how long.
Differentiate between mitigation and adaptation strategies for climate change and give two specific examples of each, indicating at what scale (local, national, or…
Differentiate between mitigation and adaptation strategies for climate change and give two specific examples of each, indicating at what scale (local, national, or global) they are applied.
The IPCC works with emissions scenarios, from the very ambitious to the very high. Explain what a climate scenario is, why science cannot announce a single future…
The IPCC works with emissions scenarios, from the very ambitious to the very high. Explain what a climate scenario is, why science cannot announce a single future temperature, and what role human decisions (energy, economy, demography) play in the range of outcomes.
Many countries have committed to "carbon neutrality" by 2050. Explain what reaching net zero emissions means, what role removals by sinks play in the balance, and why it…
Many countries have committed to "carbon neutrality" by 2050. Explain what reaching net zero emissions means, what role removals by sinks play in the balance, and why it does not mean stopping emitting altogether.
Salt marshes and Posidonia seagrass meadows store large amounts of carbon in their sediments ("blue carbon"). Explain why they are especially effective and long-lasting…
Salt marshes and Posidonia seagrass meadows store large amounts of carbon in their sediments ("blue carbon"). Explain why they are especially effective and long-lasting sinks, and discuss what happens to that carbon when a marsh is drained or a meadow is destroyed by anchoring and construction work.
Design a mitigation plan for your local area: choose three sectors (for example, energy, transportation, and carbon sinks) and justify, for each proposed action, how it…
Design a mitigation plan for your local area: choose three sectors (for example, energy, transportation, and carbon sinks) and justify, for each proposed action, how it reduces emissions or increases removals and what co-benefits it brings.