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GLOBAL GREENHOUSE GAS EMISSIONS
​At the global scale, the key greenhouse gases emitted by human activities are:
  • Carbon dioxide (CO2): Fossil fuel use is the primary source of CO2.  CO2 can also be emitted from direct human-induced impacts on forestry and other land use, such as through deforestation, land clearing for agriculture, and degradation of soils. Likewise, land can also remove CO2 from the atmosphere through reforestation, improvement of soils, and other activities.
  • Methane (CH4): Agricultural activities, waste management, energy use, and biomass burning all contribute to CH4 emissions.
  • Nitrous oxide (N2O): Agricultural activities, such as fertilizer use, are the primary source of N2O emissions. Fossil fuel combustion also generates N2O.
  • Fluorinated gases (F-gases): Industrial processes, refrigeration, and the use of a variety of consumer products contribute to emissions of F-gases, which include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).
Source: Source: IPCC (2014) based on global emissions from 2010. Intergovernmental Panel on Climate Change  via the Environmental Protection Agency U.S.A. January 2017
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2017 Global Temperatures Analysis
Excerpts from New York Times Science - January 18, 2018

...2017 Was One of the Hottest Years on Record. And That Was Without El Niño.  Researchers reported Thursday that 2017 average global temperatures are just below the record set in 2016. The result was surprising because there was no El Niño, the weather pattern usually linked to record-setting heat....
By both the NASA and NOAA analyses, 17 of the 18 warmest years since modern record-keeping began have occurred since 2001. Overall, fueled by emissions of carbon dioxide and other greenhouse gases, temperatures have increased more than 1 degree Celsius (1.8 degrees Fahrenheit) since the late 19th century.
In order to avoid the worst consequences of climate change, scientists say global temperatures must not increase more than 2 degrees Celsius...
Arctic Ice Cover
Global Annual Average Temperatures
Warming in the Arctic is causing melting of the Arctic ice pack.  The black lines represent what the climate models predict for ice cover for the future.  The red line show that the actual melting is occurring much faster than anticipated.  The melting is about 60 years ahead of the modeled result.
THE PARIS AGREEMENT - effective 11/7/16

The aim of the Agreement is described in Article 2, "enhancing the implementation" of the UNFCCC through: "
     (a) Holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and to pursue       efforts to limit the temperature increase to 1.5 °C above
pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change;
     (b) Increasing the ability to adapt to the adverse impacts of climate change and foster climate resilience and low greenhouse gas emissions development, in a manner that does not threaten food production;
     (c) Making finance flows consistent with a pathway towards low greenhouse gas emissions & climate-resilient development."
​Countries furthermore aim to reach "global peaking of greenhouse gas emissions as soon as possible". The agreement has been described as an incentive for and driver of fossil fuel divestment. 
Note Post Election 2017: Although Trump has formally withdrawn the U.S. from the Agreement, many American cities and states pledged to move forward.

While any year or decade may be warmer or cooler than the long term average, an obvious and significant increase in temperature has steadily continued.
Year to date | January through June 2017*The year-to-date average temperature was 1.64 degrees F above the 20th-century average of 56.3 degrees. This was the second-warmest for this period, 0.29 of a degree behind the record set in 2016.  
*NOAA website
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Carbon Dioxide now above 405 ppm-March 2018
PictureThe rise in global temperatures since the Industrial Revolution is clearly linked to greenhouse gas emissions/carbon dioxide.


The long lifetime of the gas means it’ll take generations before numbers below 400 ppm are revisited on the way down.
​What is Weather vs. What is Climate
While the weather can change in just a few minutes or hours, climate changes over longer time frames. Climate events, like El Niño, happen over several years, with larger fluctuations happening over decades. And, even larger climate changes happen over hundreds and thousands of years.

Today, climates are changing. Our Earth is warming more quickly than it has in the past according to the research of scientists. Hot summer days may be quite typical of climates in many regions of the world, but warming is causing Earth's average global temperature to increase. The amount of solar radiation, the chemistry of the atmosphere, clouds, and the biosphere all affect Earth's climate.

Climate Change: Present and Future  Evidence for climate change abounds, from the top of the atmosphere to the depths of the oceans. Scientists and engineers from around the world have meticulously collected this evidence, using satellites and networks of weather balloons, thermometers, buoys, and other observing systems. Evidence of climate change is also visible in the observed and measured changes in location and behavior of species and functioning of ecosystems. Taken together, this evidence tells an unambiguous story: the planet is warming, and over the last half century, this warming has been driven primarily by human activity.
Credit: NOAA; March, 2018
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