The difference between global temperatures today and the ice age is only about five degrees Celcius.
Global warming is the equivalent of a greenhouse with high efficiency reflective glass installed the wrong way around. The temperature of the earth is increasing much faster than any previous time in history.
Increased temperatures lead to the oceans, which cover most of the world's surface, to heat up. The water evaporates into the clouds, where storms like hurricanes, typhoons and tornadoes are formed, which result in more energy intensive storms.
A warmer atmosphere also makes the glaciers, mountain snow packs and polar ice caps melt, and the effect is raising sea levels. All of this makes unpredictable weather more and more common, as it changes the great patterns of wind that brings the monsoon in Asia, and rain and snow around the world, posing unique challenges to all life on earth.
Greenhouse gases are gases released by the burning of fossil fuels and the tiny particles produced by incomplete burning. It traps the sun's energy in the atmosphere.
The forms of greenhouse gases are well known.
Carbon dioxide (CO2) is produced every time something is burned.
Methane (CH4) is produced in many combustion processes and by anaerobic decomposition, for example in pigs' and cows' stomachs. These gases take about 10 years to break down, but is a precursor of the ozone layer.
Nitrous oxide (laughing gas, N2O) is a by-product of the fertiliser production process and can take up to 100 years to break down.
Fluorinated gases are replacements for ozone depleting refrigerants. It is entirely man-made and takes about 100 years to break down.
Sulphur hexafluoride (SF6) has been widely used in the fields of electronics, laser, medicine, meteorology, freezing, fire-fighting, in chemical, military, space aviation applications and non-ferrous metallurgy, and in physical research. It can take up to 1 000 years to break down.
Sources of greenhouse gases
Fossil fuels, such as coal and petroleum: The most important sources of GHGs and black carbon are power generating, industry, transportation and buildings.
Agriculture is the second most important source. This includes animals, cow and pig feed production, chemical intensive food production and deforestation to expand cultivated areas.
New studies indicate that agriculture is the largest contributor to GHGs in the US.
Where are we heading?
The visual impacts of climate change include melting glaciers, rising sea levels, flooding, worsening droughts and supercell storms.
Carbon dioxide levels has risen to 405 parts per million (ppm) in 2017 - a level that has not been seen in three to five million years. This is 46% greater than levels in the atmosphere before the industrial revolution and will cause an increase in the temperature on earth of two to three degrees Celcius, and sea levels to rise 10 to 20 metres.
Over the last 100 years alone, the average sea level rose by an estimated 20 cm. Coastal cities, such as New York, are already seeing an increased number of flooding events and by 2050 many such cities may require seawalls to survive. Estimates vary, but a rise in sea levels of 30 to 100 cm is enough to flood many small island states such as Vanuatu, famous beach resorts (Hilton Head) and coastal cities (Bangkok, Boston).
Projections suggest climate change will, within the next 100 years, if not sooner, cause the world's glaciers to disappear, as will the polar ice cap and the huge Antarctic ice shelf. Greenland may be green again, and snow will become a rare phenomenon at what are now the world's most popular ski resorts. Coral reefs also die off with the increasing heat.
Heatwaves and droughts will become more common. Hot, dry places will get hotter and drier, and places that were once temperate and had regular rainfall, will also become much hotter and much drier. The string of record high temperature years and the record number of global droughts of the past decade will become the norm. Heatwaves and droughts will increase pressure on the already fragile power, healthcare, water and sewage systems, as well as reducing countries' ability to feed themselves or export agricultural products.
The ecosystems of the world will move and change. Rising temperatures at the equator have already pushed crops such as rice north into much cooler areas. Many fish species have also migrated long distances to stay in more habitable waters.
Farmers in temperate zones are finding drier conditions difficult for crops such as corn and wheat. Once prime growing zones are now threatened and some areas will see complete ecological change.
Global population estimates suggest that developing world will add three billion people by 2050 to the planet, and that developing world food producers must more than double staple food crop production by then, simply to maintain current levels of food consumption. Food security will become a huge problem.
Curbing climate change
More than seven million people die prematurely every year due to air pollution.
Without changing diets, agriculture alone could produce enough emissions to surpass 1,5 degrees of global warming, as global meat and dairy consumption is set to increase with close to 70% by 2050.
Rising temperatures favour agricultural pests, diseases and disease vectors. Pest populations are on the rise and illnesses once only found in limited tropical areas are now becoming endemic in much wider zones.
Higher temperatures also increase the reproduction rates of microbes and insects, speeding up the rate at which they develop resistance to control measures and drugs, a problem already observed with malaria in Southeast Asia. With unpredictable climate change, rising sea levels, a challenge to grow crops, changes in the range in which plants, animals and humans can survive, and the loss of water supplies that have come from glaciers, earth can become a very quiet place if we don't start doing something about it.
