Greenhouse gas emissions is the general description for release to the atmosphere of a cluster of gases that absorb some of the long-wave radiation that has bounced off the earth’s surface. This property of a handful of gases traps energy that would otherwise radiate back into space creating a ‘greenhouse effect’.
The important greenhouse gases [in order of 100 year global warming potential potency, i.e. their capacity to trap energy] are:
And before we see these gases entirely as nasty pollutants it is worth remembering that without them the earth would be a giant snowball with not enough free water to sustain life.
Over geological time the proportions of greenhouse gases in the atmosphere have fluctuated. One of the biggest changes followed the development and spread of land plants around 500 million years ago — before photosynthesis really got going in earnest there was not enough oxygen in the atmosphere to sustain a fire. Nor was there much fuel to burn.
Then, of course, the fluorocarbons are man made. Once in the atmosphere they also happen to be the most potent at trapping energy.
We know that fluctuations in greenhouse gas concentrations have had a strong influence on global climate. The specifics are complicated but the amount of energy retained in the atmosphere drives cycles of temperature and moisture that in turn determine weather patterns.
And so we arrive at a critical assumption.
cattle are a significant source of methane that is produced as microbial activity in their stomachs breaks down the coarse grass that they eat
Greenhouse gas emissions from human activity have enhanced the greenhouse effect and led to a warming of the climate — greater concentrations trapping more energy.
The majority of climate scientists agree with this assumption.
It also underpins the latest IPCC 30-year projection for 0.3 to 0.7 degrees C of warming above the current averages.
Less of an assumption is the recent changes to atmospheric composition. We know that human activity [especially burning fossil fuels, clearing land for agriculture, fertilizer use and methane from cattle and landfill] has added greenhouse gas emissions since the start of the industrial revolution because we can a) reliably estimate these emissions and b) measure the atmosphere.
We also know that current global greenhouse gas emissions are at 31,350 million tCO2e per year. At this rate concentrations in the atmosphere will continue to increase for this amount is greater than the buffering capacity of soil, vegetation and the oceans.
Too much greenhouse effect is not good. It causes no end of difficulties. Direct effects of flood, drought and storm and indirect effects for water supply, agricultural production, disease… the list is long.
In effect excess greenhouse gases are a pollutant.
If the environmental issue is too much greenhouse gas then the obvious solution is to curb greenhouse gas emissions.
Again most scientists either explicitly or implicitly agree with this assumption. The smart ones concede that whilst the logic is sound there are many unknown lags and feedback mechanisms that defy a simple one to one effect.
It is certain not the case that if the concentration is reduced [or more realistically the increase in concentrations slowed] it will reverse climate changes overnight.
The evidence s sound enough for the precautionary principle to hold — when in doubt, stop making a mess.
this grazing property in NSW sequesters more than the usual amount of carbon into trees, grasses and soil because grazing is carefully managed
There are observers, notably the ‘skeptical environmantalist’ Bjorn Lomberg, who whilst conceding that climate change is a major environmental issue, it is not the only one. There are many more important issues to tackle.
It may well be better to invest in resolving more acute issues, especially those that also confer some climate resilience such as soil degradation, water use efficiency, and best practice land management.
In other words, pick your fights carefully.
gases are exchanged between the atmosphere and oceans
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