What is Global Warming and Climate Change?

Global warming and climate change refer to an increase in average global temperatures. Natural events and human activities are believed to be contributing to an increase in average global temperatures. This is caused primarily by increases in greenhouse gases such as Carbon Dioxide (CO2).

A warming planet thus leads to a change in climate which can affect weather in various ways, as discussed further below.

What are the main indicators of Climate Change?

As explained by the US agency, the National Oceanic and Atmospheric Administration (NOAA), there are 7 indicators that would be expected to increase in a warming world (and they are), and 3 indicators would be expected to decrease (and they are):

Air temperature near surface, humidity, temperature over oceans, sea surface temperature, sea levels, ocean heat content and temperature over land are all increasing, while glaciers, snow cover and sea ice are all decreasing.
Ten indicators for a warming world, Past Decade Warmest on Record According to Scientists in 48 Countries, NOAA, July 28, 2010

What is the Greenhouse Effect?

The term greenhouse is used in conjunction with the phenomenon known as the greenhouse effect.

  • Energy from the sun drives the earth’s weather and climate, and heats the earth’s surface;
  • In turn, the earth radiates energy back into space;
  • Some atmospheric gases (water vapor, carbon dioxide, and other gases) trap some of the outgoing energy, retaining heat somewhat like the glass panels of a greenhouse;
  • These gases are therefore known as greenhouse gases;
  • The greenhouse effect is the rise in temperature on Earth as certain gases in the atmosphere trap energy.
Image source: Greenhouse Effect, Wikipedia
(Link includes detailed explanation of the above image). Note, image above expresses energy exchanges in watts per square meter (W/m2)

Six main greenhouse gases are carbon dioxide (CO2), methane (CH4) (which is 20 times as potent a greenhouse gas as carbon dioxide) and nitrous oxide (N2O), plus three fluorinated industrial gases: hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride (SF6). Water vapor is also considered a greenhouse gas.

The Greenhouse effect is natural. What do we have to do with it?

Many of these greenhouse gases are actually life-enabling, for without them, heat would escape back into space and the Earth’s average temperature would be a lot colder.

However, if the greenhouse effect becomes stronger, then more heat gets trapped than needed, and the Earth might become less habitable for humans, plants and animals.

Carbon dioxide, though not the most potent of greenhouse gases, is the most significant one. Human activity has caused an imbalance in the natural cycle of the greenhouse effect and related processes. NASA’s Earth Observatory is worth quoting the effect human activity is having on the natural carbon cycle, for example:

In addition to the natural fluxes of carbon through the Earth system, anthropogenic (human) activities, particularly fossil fuel burning and deforestation, are also releasing carbon dioxide into the atmosphere.

When we mine coal and extract oil from the Earth’s crust, and then burn these fossil fuels for transportation, heating, cooking, electricity, and manufacturing, we are effectively moving carbon more rapidly into the atmosphere than is being removed naturally through the sedimentation of carbon, ultimately causing atmospheric carbon dioxide concentrations to increase.

Also, by clearing forests to support agriculture, we are transferring carbon from living biomass into the atmosphere (dry wood is about 50 percent carbon).

The result is that humans are adding ever-increasing amounts of extra carbon dioxide into the atmosphere. Because of this, atmospheric carbon dioxide concentrations are higher today than they have been over the last half-million years or longer.

The Carbon Cycle; The Human Role, Earth Observatory, NASA

Another way of looking at this is with a simple analogy: consider salt and human health:

  • A small amount of salt is essential for human life;
  • Slightly more salt in our diet often makes food tastier;
  • Too much salt can be harmful to our health.

In a similar way, greenhouse gases are essential for our planet; the planet may be able to deal with slightly increased levels of such gases, but too much will affect the health of the whole planet.

Image source: NASA.(Note, values shown represent Carbon Gigatons being absorbed and released)

The other difference between the natural carbon cycle and human-induced climate change is that the latter is rapid. This means that ecosystems have less chance of adapting to the changes that will result and so the effects felt will be worse and more dramatic it things continue along the current trajectory.

The climate has always varied in the past. How is this any different?

Throughout Earth’s history the climate has varied, sometimes considerably. Past warming does not automatically mean that today’s warming is therefore also natural. Recent warming has been shown to be due to human industrialization processes.

John Cook, writing the popular Skeptical Science blog, summarizes the key indicators of a human finger print on climate change:

Less heat escaping to space, shrinking thermosphere, cooling stratosphere, rising tropopause, less oxygen in the air, more fossil fuel carbon in the air, 30 billion tonnes of C02 per year, more heat returning to Earth, nights warming faster than days, and more fossil fuel carbon in coral are all signs of human-induced climate change.
John Cook, 10 Indicators of a Human Fingerprint on Climate Change, Skeptical Science, July 30, 2010

This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the Industrial Revolution:

Only in the past few decades has the amount of Carbon Dioxide dramatically increased to levels not seen in the past 650,000 years
(Source: NOAA) via: Climate Change: How do we know? NASA, accessed October 27, 2009

The above covers hundreds of thousands of years and shows how atmospheric CO2 levels have dramatically increased in recent years. If we zoom in on just the past 250 years, we see the following:

Emissions significantly increase in the past 100 years. The graph almost looks like an exponential curve
Global CO2 emissions, 1751–2010, Carbon Dioxide Information Analysis Center (CDIAC), 2013, last accessed February 1, 2015. DOI:10.3334/CDIAC/00001_V2013

NASA’s Goddard Institute of Space Studies (GISS) tracks atmospheric global temperature climate trends. As environmental engineer, D Kelly O’Day, explained on ProcessingTrends.com (link no longer available): To facilitate assessments of long term trends, climatologists compare the mean for a base period with the annual mean. Differences between the annual mean and baseline mean are called anomalies. GISS uses the 1951 – 1980 period for their baseline period. They use the difference between the annual mean and the baseline mean to determine the global temperature anomaly for the year.

O’Day originally produced a chart showing global temperature anomalies between 1800 and 2006 using data from NASA. I updated the chart he provided to include recently updated data up to 2014:

Sources: GISS Surface Temperature Analysis, NASA, accessed January 25, 2015; Global temperature, 1800-2006, ProcessTrends.com, accessed October 27, 2009 (link no longer available)

In the 1880 – 1935 period, the temperature anomaly was consistently negative. In contrast, the since 1980 the anomaly has been consistently positive. The 1909 temperature anomaly (-0.47oC) was the lowest year on record. Since 1909, global temperature has warmed, with the most recent years showing the highest anomalies of +0.6 oC in the past 120 years.

A NASA’s GISS animation also shows how most parts of the world have experienced this warming, recently:

Global temperatures have warmed significantly since 1880, the beginning of what scientists call the modern record. At this time, the coverage provided by weather stations allowed for essentially global temperature data. As greenhouse gas emissions from energy production, industry and vehicles have increased, temperatures have climbed, most notably since the late 1970s. Source: NASA Finds 2014 Warmest Year in Modern Record, NASA Goddard Institute for Space Studies, January 16, 2015

And, as Sir David Attenborough explains, natural variability alone does not explain recent temperature rise:

Sir David Attenborough: The Truth About Climate Change, October 22, 2006

As well as the links above, see also Skeptical Science, which, while examining the arguments of global warming skepticism, provides information on causes of anthropogenic global warming.

Doesn’t recent record cold weather disprove Global Warming?

In different parts of the world, there have been various weather events that at first thought would question global warming. For example, some regions have experienced extremely cold winters (sometimes record-breaking), while others have experienced heavy rain, etc.

The confusion that sometimes arises is the difference between climate change and weather patterns. Weather patterns describe short term events, while climate change is a longer process that affects the weather. A warming planet is actually consistent with increasing cold, increasing rain and other extremes, as an overall warmer planet changes weather patterns everywhere at all times of the year.

To get an idea of how looking at short term changes only can lead to a conclusion that global warming has stopped, or doesn’t exist, see Alden Griffith’s has global warming stopped?

(As an aside, those crying foul of global warming claims when going through extremely cold weather in Europe for example in 2010, later found their summers to be full of heat waves. The point here is that a specific short period such as a cold winter — or even a hot summer — is not proof alone that global warming has stopped (or increased); short term variability can mask longer term trends.)

This means, for example, increasing temperatures can actually mean more snowfall — at least until it becomes too warmfor significant snowfall to happen.

The additional concern, as meteorology professor Scott Mandia explains, it can take decades for the climate temperatures to increase in response to increased greenhouse gas emissions. So up until now, perhaps it has been easier for skeptics to deny climate change is occurring or that humans are responsible.



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