This article contains video clip and an article (to be upleaded shortly). It is an overview of global warming. This article or video is not all inclusive. It is to describe the general effects of global warming.
Global warming a simple overview
Introduction:
Global warming exists. It has existed for thousands and thousands of years. The question is what impact is man-made gases and industrialization having on the planets natural balance. This paper, blog and video will discuss the natural occurrence of global warming and cooling as well as take a look at the science behind the industrial revolution and the causes it has on the atmosphere and ocean temperatures.
Global warming is occurring on our planet. The temperature on earth has gone through many cycles of warming and cooling often called glacier and inter glacier periods. These past cycles have been a natural occurrence of our planet. When the industrial revolution began humans began to add to the natural occurrence gases that cause the earth atmosphere and ocean to rise in temperature.
This overview will go through the natural cycles the planet goes through and also the impact that modern society is having.
Earths Orbit-
Eccentricity- the earth’s orbit is not circular but is elliptical and changes shape from near circular to elliptical. This cycle of going from near circular to elliptical orbit takes about 100,000 years.
In an elliptical orbit:
Perihelion – is the closet point to the sun (more solar radiation)
Aphelion – is the farthest point from the sun (less solar radiation)
Obliquity- is the angle of the earth’s axis is tilted in regard to the orbit. It varies from 22.1 degrees to 24.5 degrees and this cycle takes about 45,000 years to complete. This gives rise to the seasons.
At 22.1 degree tilt the summers are cooler and winters milder
At 24.5 degree tilt the season are more extreme summers hotter and winters colder.
Precession- is the change in the direction the axis is pointing. This takes about 21,000 years. It traces a cone shape. Now we have the Northern Hemisphere pointing towards the sun in summer and away from the sun in the winter. In about 11,000 years the Northern Hemisphere will be pointing away from the sun in the summer (that will then be our winter) and towards the sun in the winter (that will then be our summer).
Sun
The sun also has cycles it goes through. Every 11 years or so there is a rise in solar flares. (This can be seen in the rise of northern light activity.) The sun also has sunspots – which block solar radiation and faculae spots, which increase solar radiation.
Layers of the atmosphere –
Layers of the earths atmosphere is
Troposphere – up to 20 km this is where we live and fly planes
Stratosphere - up to 50 km the Ozone layer is here (we will talk about the ozone layer in a few minutes).
Mesosphere – up to 85km
Thermosphere – up to 300km the space shuttle
Exosphere – up to 10,000 km
It is the Troposphere and the stratosphere that we will be mainly talking about with greenhouse gases and ozone depletion.
Ice cores
So how do we know what the earth was like in the past? What was the climate like and what was the atmosphere made up of. If we could only see into the past. Well the remarkable thing is we can. Ice core sample from Greenland and the Antarctic (the main ones) have given us a look into the past.
From these ice cores there where times of warming and times of ice ages. The corresponding levels of CO2 are representative of:
Higher levels mean higher temperatures
Lower levels of CO2 mean lower temperatures
It looks like the temperatures in the past began to rise then the levels of CO2 began to rise.
CO2 levels currently are at about 380 parts per million
In the past they have been in the range of 200 – 300 parts per million
Methane levels currently are at about 1,800 parts per billon.
In the past the levels have been in the range of 400 – 700 parts per billon
The latest information is from Nature High-resolution carbon dioxide concentration record 650,000 – 800,00 years before present.
Green house gases and the atmosphere-
Water vapor
Carbon dioxide
Methane
Nitrous oxide
Ozone
CFCs
These gases do absorb radiation. This is what makes them a green house gas. There is a natural level of these gases in the atmosphere (except for CFCs). Without these gases naturally present the earth would be much colder and inhabitable.
Methane is a stronger green house gas but is in much smaller quantities than carbon dioxide. This makes carbon dioxide a much larger threat to global warming.
Both CO2 and Methane vary between glacial and interglacial phases and concentrations correlate strongly with temperatures. The CO2 levels began to rise after temperature began to rise.
Sources and sinks - as the temperature decreases the ocean is colder and can absorb more CO2 (the ocean is a sink).
As the temperature warms more CO2 is released into the atmosphere. This further increases the global temperature. It is a loop that keeps s feeding itself, a positive feedback loop.
Greenhouse effect –
Radiation is reflected back into the atmosphere and absorbed and radiated back from the surface. The radiation that needs to escape from the atmosphere and back into space to help cool the atmosphere down. There is an infrared window.
Infrared window –
Part of the electromagnetic spectrum that are not absorbed at all. This window lies in the range of 8 and 14 micrometers. The radiation emitted by the earth in this range pass through the window without heating the atmosphere and leave into space. This window is critical otherwise the earth would heat too much and would result in a Venus like atmosphere (one that is not habitable).
Some of the manmade compounds are absorbing radiation in this window. There is no sink for some of these compounds. Thus making them a more dangerous greenhouse gas than say CO2, which does have some natural sinks (and sources as well as man made sources).
Ozone depletion –
Ozone in the stratosphere is being depleted by about 4% a year. The ozone layer is needed to reflect harmful UVB radiation (270 – 315 nm wavelength). With the ozone layer being depleted this allows more radiation in. (More radiation in and less radiation allowed to escape is causing the earth atmosphere and oceans to heat hence a global warming effect.)
The main compounds that destroy ozone in the stratosphere are:
CFC – chlorofluorocarbon (freons)
Bromofluorocarbon (halons)
Carbon tetrachloride
Tricholorethane
These have been banned by the Montreal Protocol but many of these compounds last for decades to hundreds and some last thousands of years. They will continue to do damage to the Ozone layer in the stratosphere for many thousands of years.