The Causes of Climate Change
In Monterrey, on a July day, the temperature inside a car parked in the sun with the windows closed reaches 50 °C, while it is much cooler outside. What is happening in the air all around the planet that is similar to that car, and why are we worried today that it is becoming more "closed in"?
The natural greenhouse effect
Inside the car, the glass lets sunlight in but traps heat. On Earth, some gases in the atmosphere do something similar. Before we look at the problem, it helps to tell two words apart: weather is the state of the atmosphere at a given place and time (today it is raining in Oaxaca); climate is the average pattern over many years (in Oaxaca it rains mostly from June to September).
Explain the difference between weather and climate, and give an example of each.
Explain the difference between weather and climate, and give an example of each.
The diagram represents the greenhouse effect in four numbered steps. a) Explain what happens in each of the steps labelled with the numbers 1 to 4. b) Which number…
The diagram represents the greenhouse effect in four numbered steps.
- a) Explain what happens in each of the steps labelled with the numbers 1 to 4.
- b) Which number corresponds to the heat returned by the atmosphere towards the surface?
- c) Name two greenhouse gases.
The greenhouse effect is a natural phenomenon necessary for life. Explain why this is so and clarify the current problem (the enhanced greenhouse effect due to human…
The greenhouse effect is a natural phenomenon necessary for life. Explain why this is so and clarify the current problem (the enhanced greenhouse effect due to human emissions).
Consumption practices that disrupt the cycles
Carbon circulates among the atmosphere, living things, and the soil: plants take it in through photosynthesis, and it returns to the air through respiration and decomposition. This cycle used to be in balance. Our consumption practices disrupt it.
The nitrogen cycle is also disrupted
Nitrogen ($\text{N}_2$) makes up most of the air, but almost no living thing can use it in that form. In nature it circulates in three steps: fixation (soil bacteria, such as those living in bean roots, convert it into compounds that plants can use), nitrification (other bacteria transform those compounds into nitrates, which plants absorb), and denitrification (other bacteria return nitrogen to the air). That is why, in the milpa, beans help the corn.
When fertilizers are applied in excess, the soil receives more nitrogen than plants can use, and bacteria transform it into nitrous oxide ($\text{N}_2\text{O}$), a greenhouse gas. Livestock manure and the burning of vegetation also add nitrogen and gases to the air.
Not all gases warm equally
Each gas has two characteristics: how much it warms and how long it lasts in the atmosphere. $\text{CH}_4$ warms much more than $\text{CO}_2$ (about 80 times more over 20 years), but it disappears in about 12 years. $\text{CO}_2$ warms less per molecule, but it stays for centuries. So, reducing methane gives quick relief, and reducing $\text{CO}_2$ is what slows warming in the long term.
Name three human activities that increase emissions of greenhouse gases into the atmosphere.
Name three human activities that increase emissions of greenhouse gases into the atmosphere.
How is deforestation linked to climate change? Reason two different mechanisms: the reduced absorption of $\text{CO}2$ and the emissions caused by cutting down or…
How is deforestation linked to climate change? Reason two different mechanisms: the reduced absorption of $\text{CO}_2$ and the emissions caused by cutting down or burning forests.
The concentration of atmospheric $\text{CO}2$ was 317 ppm in 1960, 354 ppm in 1990, and 414 ppm in 2020. Calculate the increase between 1960 and 2020, express it as a…
The concentration of atmospheric $\text{CO}_2$ was 317 ppm in 1960, 354 ppm in 1990, and 414 ppm in 2020. Calculate the increase between 1960 and 2020, express it as a percentage, and relate the trend to human activities.
Processes that amplify warming
A white T-shirt feels cool in the sun and a black one feels scorching. What happens in the Arctic when the white ice melts and exposes the dark sea?
Analyse the following global temperature anomaly data: −0.2 °C in 1880, +0.2 °C in 1980, and +1.2 °C in 2023. Calculate the average warming rate per decade in the period…
Analyse the following global temperature anomaly data: −0.2 °C in 1880, +0.2 °C in 1980, and +1.2 °C in 2023. Calculate the average warming rate per decade in the period 1880-1980 compared to the period 1980-2023. Based on the result, justify whether global warming follows a constant or an accelerated progression, and predict what temperature anomaly we would reach in 2050 if the rate of the last period were maintained compared to if the rate of the first had been maintained.
An advisory team proposes two strategies to curb global warming before 2040: Plan A aims to eliminate natural gas leaks and reduce intensive livestock herds (focusing on…
An advisory team proposes two strategies to curb global warming before 2040: Plan A aims to eliminate natural gas leaks and reduce intensive livestock herds (focusing on methane, $\text{CH}_4$); Plan B focuses on decommissioning coal-fired power plants (focusing on $\text{CO}_2$). Knowing that $\text{CH}_4$ warms about 80 times more than $\text{CO}_2$ over a 20-year timescale but disappears from the atmosphere in about 12 years, while $\text{CO}_2$ remains for centuries, evaluate which of the two plans would slow down warming faster in the short term and which one is essential to prevent irreversible change in the long term. Justify your verdict.
In a school debate, someone argues: «In the Cretaceous there was no ice at the poles and the Earth was much warmer than today without human intervention; therefore, the…
In a school debate, someone argues: «In the Cretaceous there was no ice at the poles and the Earth was much warmer than today without human intervention; therefore, the current warming is natural and we should not worry». Refute this statement by comparing the timescale (rate) at which those geological changes occurred versus that of the current change, and explain what direct consequence this difference in speed has on the adaptive capacity of ecosystems and species survival.
Back to the beginning: the car in the sun in Monterrey traps heat because the glass lets light through and traps the heat; the atmosphere does the same thing with greenhouse gases, and our emissions are "closing it in" more.