Human Impacts: CO2, Global Warming

CARBON DIOXIDE and GLOBAL WARMING

PAST TEMPERATURES:
The best way to estimate temperatures of the past is by oxygen isotope ratios.
- Different isotopes of oxygen have slightly different solubility levels in ocean water at different temperatures, so the ratio of oxygen isotopes can be used as a measure of ocean temperature.
- Various single-celled organisms (especially Foraminifera and Radiolaria) and multicellular animals (such as clams) build shells of calcium carbonate (CaCO₃), and the oxygen isotopes in these shells reflect the oxygen isotopes in the sea water at the time the shells were secreted.
- Using oxygen isotope ratios, the Italian-American scientists Cesare Emiliani was able to document ancient ocean temperatures as far back as the Jurassic.
PAST CO₂ LEVELS:
Ice cores taken from large glaciers in Greenland and Antarctica contain tiny bubbles of trapped air from the time that the ice was formed.
Carbon dioxide levels can be measured in these bubbles and show similar values from glaciers in different parts of the world.
The record of CO₂ levels from these ice cores goes back tens of thousands of years.
Over the last few thousand years, records from around the world are more numerous, and they show simultaneous
highs and lows everywhere, meaning that the CO₂ levels were worldwide and not local.
Comparison of temperature and CO₂ records:
Comparison of temperature and CO₂ records from various sources shows clearly that higher CO₂ levels always accompanied higher temperatures,
and low CO₂ levels always accompanied lower temperatures.
Both CO₂ levels and temperatures increased very slowly over the last 8,000 years or so.
CO₂ levels and temperatures both increased much more rapidly beginning at the start of the Industrial Revolution (around 1800).
The rate of increase accelerated (it increased more steeply) throughout the twentieth century.

CO₂ and CLIMATE CHANGE

GREENHOUSE EFFECT:
All forms of electromagnetic energy can excite molecules and make them move faster, creating heat.
If light or other electromagnetic energy enters a greenhouse, the heat energy is trapped inside the greenhouse and cannot escape.
This warms the greenhouse, producing a greenhouse effect.
Earth's atmosphere acts like a greenhouse. Electromagnetic energy from the sun excites the molecules in the atmosphere and causes them to move faster, creating heat.
This traps heat within the atmosphere, producing a greenhouse effect.
Some molecules in the atmosphere, like CO₂, contribute more than others to the greenhouse effect.
A few molecules, like methane, have a much larger per-gram greenhouse effect, but their quantities are so low that we usually ignore them.
The greenhouse effect warms the planet and is the major reason for global warming.
CARBON DIOXIDE POLLUTION:
Scientists who measure climates of the past (see above) have concluded that
temperatures of the past have always gone up with higher CO₂ concentrations and down with lower CO₂ concentrations.
Since the 1950s, Nobel Prize-winning scientist Charles Keeling has been measuring CO₂ concentrations at Mauna Loa Observatory on Hawaii.
This location is in the middle of the Pacific, far from any industrial source of pollution, and is widely thought to represent global averages of CO₂ concentrations.
Keeling's measurements show that CO₂ concentrations go up and down seasonally (lower in summer, when plant photosynthesis removes more CO₂ from
the atmosphere, and higher in winter), but the overall year-to-year trend has been steadily upward since the 1950s !
Global average temperatures have also been rising steadily over this same time period. In most places, the hottest years on record are mostly the recent ones.
Most scientists attribute the rise in CO₂ concentrations to the release of combustion products (mostly from the use of fossil fuels),
and the increase in global average temperatures to the greenhouse effect.
Feedback effects:
As temperatures rise, the melting of polar ice lowers the planet's albedo, meaning that more solar energy is absorbed by the dark-colored rocks and soil
instead of being reflected out to space by the ice. This contributes to more global warming.
The melting of polar ice also releases significant quantities of methane gas and complex methane compounds (clathrates) frozen inside.
Although the quantites are small, methane is a very potent greenhouse gas, several hundred times as strong as CO₂ in contributing to the greenhouse effect.
As temperatures rise, forest fires are becoming more frequent, larger, and harder to contain. Forest fires contribute to the rise in atmospheric CO₂.
The loss of forest vegetation also contributes to higher CO₂ concentrations because plant photosynthesis no longer removes CO₂ from the atmosphere.
All of the above contribute to feedback: increased global warming contributes to even more global warming!
Other consequences:
As global temperatures rise, more polar ice melts, and this contributes to rising sea levels.
In 2019, an iceberg the size of Delaware broke off Antarctica and began to drift toward warmer waters, where it will eventually melt and add to global sea rise. Similar icebergs, large and small, are breaking off the edge of both Greenland and Antarctica at increasing rates.
As carbon dioxide contrations rise, more of it dissolves in sea water and forms carbonic acid, making the waters more acidic.
This ocean acidification contributes to the death of corals. Colorful coral reefs turn white, and this is called coral bleaching.
And it isn't just the corals: coral reefs are the most diverse aquatic habitats on the planet, containing a larger fraction of biodiversity than any other aquatic habitat!

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