Take a deep breath.
If you are about as old as I am, that breath contains about 25% more CO2
than your first breath. Each breath
today has about 45% more CO2 than when George Washington was alive. CO2 is rapidly accumulating in the atmosphere
due to the use of fossil fuels. In the
ten years I have been writing about global CO2, I have had to change those
figures several times.
The world is warming.
For over 150 years, scientists have known that greenhouse gases such as
CO2 and methane warm the atmosphere by retaining heat from the sun. The use of fossil fuels has raised the
average concentration of CO2 in the atmosphere from about 280 ppm to over 400
ppm.
“Global Warming” generally means the direct warming of the
earth due to greenhouse gases in the atmosphere. “Climate Change” usually refers to the myriad
second-order effects which result from the retained heat.
Heat retained by greenhouse gases causes many changes:
changes in atmospheric circulation, changes in the patterns of winds, rising
sea level, changes in the location of deserts, changes in the amount and intensity
of rainfall, decrease in annual snow cover, changes to the timing of seasons
and animal migrations, warming permafrost, changes in plant hardiness zones for
home gardeners, etc.
The most direct measure of climate change is the rising heat
in natural systems – the oceans, ice caps, sea ice, glaciers and
atmosphere.
Oceans
The oceans are warming.
We know because we are taking the temperature of the oceans.
ARGO is a scientific project run by a consortium of over 30
nations begun in the early 2000s. The
project consists of nearly 4000 buoys, which dive to a depth of 2000 meters
every ten days and return to the surface, taking the temperature of the ocean
to an accuracy of 0.002 degrees C. Data
is broadcast to satellites. Combining
the ARGO data with early studies, we see that the upper 100 meters of ocean
have warmed by 0.5 degrees C since 1970.
Temperature changes at depth are smaller, showing that the heat is
originating at the ocean surface, and propagating downwards. The rising heat content of the oceans
accounts for about 95% of the heat trapped in the atmosphere by greenhouse
gases.
Ice
Ice is melting around the globe.
Scientific studies of Antarctica began in earnest in the
International Geophysical Year, 1957. By
the 1990s, it was recognized that the Antarctic ice cap was melting. In 2003, NASA launched the GRACE satellite
experiment to measure the ice loss from Antarctica and Greenland using gravity
measurements. Combined with earlier
observations, the new data shows a clear loss of ice from Antarctica.
Ice is also disappearing from Greenland. A seasonal fluctuation is seen clearly in the
data.
Arctic sea ice is disappearing. The area covered by sea ice, also monitored
by satellite, has shrunk dramatically in recent decades. The thickness and age of the sea ice has also
declined, as well as sea ice in the neighboring Bering Sea.
Continental glaciers are shrinking. The World Glacier Monitoring Service, an
agency of the United Nations, has been monitoring glaciers since the
mid-1940s. As anyone who lives in Alaska
knows, glaciers have been steadily receding over recent decades, and the loss
of ice can often be noticed from year-to-year.
Overall, the volumes of ice lost from Antarctica, Greenland,
Arctic Sea Ice and Continental Glaciers account for about 3% of the heat
retained by greenhouse gases.
Atmosphere
The atmosphere is warming.
The rising temperature of the atmosphere, which is sometimes
questioned by climate change deniers, is actually the least significant of the
earth’s heat sinks. Only about 1% of the
heat retained by greenhouse gases actually remains in the atmosphere. Nevertheless, the atmosphere is noticeably
warming. The warmest year on record was
2016. Seventeen out of eighteen of the
warmest years in the 136-year record have occurred since 2001.
The evidence for heat retained by greenhouse gases is
comprehensive and compelling. The amount
of heat retained by greenhouse gases is in close agreement with the rising heat
observed in the earth’s oceans, in melting ice, and the warming
atmosphere.
The consequence of global warming is climate change. In future posts, we can look at the
detrimental impact of excess heat on people and the environment.
References
Oceans
ARGO
NOAA Ocean Temperature and Heat Content
Ice
NASA GRACE Ice Mass, Antarctica and Greenland
Integrated Methods Measuring Ice Mass
Atmosphere
NASA
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