Earth's Systems / Energy flow / Greenhouse trapping and release to space / Atmospheric chemistry: methane removal and the ozone layer
Atmospheric chemistry: methane removal and the ozone layer
Chemistry in the air sets how long greenhouse gases last and how much ultraviolet light reaches the surface. Hydroxyl radicals break down methane in about nine years, and the Montreal Protocol is letting the stratospheric ozone layer recover.
Boundary: where this process starts
Starts with: Hydroxyl radicals (OH) break down methane, giving it a lifetime of about 9 years
Boundary: where it ends
Ends after: Hydroxyl radicals (OH) break down methane, giving it a lifetime of about 9 years; Cutting ozone-depleting gases under the Montreal Protocol lets ozone return to 1980 levels around 2040 globally, 2045 in the Arctic and 2066 over Antarctica
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
- Participant
- Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
- Resource
- Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
- Step
- One thing that happens in a process. Every step has at least one participant and carries evidence.
- Decision fork
- A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
- Loop
- A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
- Size of impact
- Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
- Evidence
- The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
- Boundary
- Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
- Subprocess
- A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
- Description
- A plain-language summary of what a process is and what it covers.
- Hypothesis
- A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.
Every step, with its evidence
The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.
Hydroxyl radicals (OH) break down methane, giving it a lifetime of about 9 years
Evidence (1) · added by Gable
- Nicely et al. 2018, J. Geophys. Res. Atmos., https://doi.org/10.1029/2018JD028388, as summarised by NASA at https://science.nasa.gov/earth/earth-atmosphere/greenhouse-gas-detergent-recycles-itself-in-atmosphere-nasa-study/: OH is the main check on methane; methane's lifetime is currently estimated at nine years. (confidence 0.8)
OH is recycled by nitrogen oxides and replenished as the tropics widen, so its level stayed roughly steady from 1980 to 2015 despite more methane
Evidence (1) · added by Gable
- Nicely et al. 2018, J. Geophys. Res. Atmos., https://doi.org/10.1029/2018JD028388, as summarised by NASA at https://science.nasa.gov/earth/earth-atmosphere/greenhouse-gas-detergent-recycles-itself-in-atmosphere-nasa-study/: Recycling via NO and NO2 and tropical widening (0.5-1 degree latitude per decade) together essentially replace the OH used up breaking down methane (satellite data 1980-2015). (confidence 0.75)
Cutting ozone-depleting gases under the Montreal Protocol lets ozone return to 1980 levels around 2040 globally, 2045 in the Arctic and 2066 over Antarctica
Evidence (1) · added by Gable
- WMO/UNEP Scientific Assessment of Ozone Depletion 2022, Executive Summary, https://csl.noaa.gov/assessments/ozone/2022/executivesummary/: Near-global ozone returns to 1980 values around 2040, Arctic around 2045, Antarctic around 2066; avoided ozone-depleting emissions avoid about 0.5-1 C of warming by mid-century. (confidence 0.85)