2 Global warming

Global warming is a long-term trend of increasing global average temperature. We still have weather, which causes fluctuations around a rising trend line. Those who live in areas with distinct seasons are well aware of this. A new season brings a much faster change than global warming does. The principle is basically the same. In the spring, a cold front may cool the weather a week or two. But most people realize, however, that summer is coming. The cooling period is just a skip down for a while before we get back to a rising temperature after the trend line.

Average monthly temperatures may vary  from one year to the next by 5-6 degrees.  This is weather variation. Global average temperature increase has roughly been slightly less than 0,2° C per decade, or less than 0,02° C on average per year over the last decades – for the time being. That is the climate trend. This is why you should not confuse weather with climate. When you want to take a closer look at climate trends, you go to the baseline: the Normal, and compare average weather over at least five years to this baseline.  Any period shorter than this is weather variations and not climate. –The Normal is calculated for a period of 30 years.

decadal warming

When measuring the average temperature over decades, there is a clear warming.. Global warming the last three decades has been dramatic. Source: World Meteorological Organisation, 2013

Temperature rise accelerates

For the last 50 years, global temperature rose at an average rate of about 0.13°C (around one-quarter degree Fahrenheit) per decade—around twice as fast as the 0.06°C per decade increase observed over the previous half-century. In the next 20 years, scientists project that global average temperature will rise by around 0.2°C (about one-third of a degree Fahrenheit) per decade (NOAA 2016).

multigraph

 ” The average global temperature across land and ocean surface areas for 2015 was 0.90°C (1.62°F) above the 20th century average of 13.9°C (57.0°F), beating the previous record warmth of 2014 by 0.16°C (0.29°F). This is not only the highest calendar year temperature, but also the highest temperature for any 12-month period on record. ”

2015 record hot

2015 has clearly been warmer than 2014, although northern Europe has not had a particularly hot summer. The rest of the world has had an exceptionally warm period.

201501-201512 (2)

The 16 warmest years that have been recorded during the period between 1880 -2015, all occurred in this century, except 1998, which tied as the sixth warmest. (National Oceanic and Atmospheric Administration, 2016)

2016 even warmer

BBC (2016) Six graphics that explain climate change

twelve warmest years

NOAA: Global climate report 2016

fig-1-a-better-graph-620x442

Hansen, J. (2016) Global surface temperature relative to 1880-1920 based on GISTEMP analysis (mostly NOAA data sources, as described by Hansen, J., R. Ruedy, M. Sato, and K. Lo, 2010: Global surface temperature change. Rev. Geophys., 48, RG4004. We suggest in an upcoming paper that the temperature in 1940-45 is exaggerated because of data inhomogeneity in WW II. Linear-fit to temperature since 1970 yields present temperature of 1.06°C, which is perhaps our best estimate of warming since the preindustrial period

According to NASA (2016) , “the Earth’s climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives. The current warming trend is of particular significance because most of it is very likely human-induced and proceeding at a rate that is unprecedented in the past 1,300 years.1

Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate”.

Earth’s 2015 surface temperatures were the warmest since modern record keeping began in 1880, according to independent analyses by NASA and the National Oceanic and Atmospheric Administration (NOAA). Globally-averaged temperatures in 2015 shattered the previous mark set in 2014 by 0.23 degrees Fahrenheit (0.13 Celsius). Only once before, in 1998, has the new record been greater than the old record by this much.
This color-coded map displays a progression of changing global surface temperature anomalies from 1880 through 2015. Higher than normal temperatures are shown in red and lower then normal termperatures are shown in blue. The final frame represents the global temperatures 5-year averaged from 2011 through 2015. Scale in degree Celsius.

NASA/Goddard Space Flight Center Scientific Visualization Studio. Data provided by Robert B. Schmunk (NASA/GSFC GISS).

There is a clear scientific consensus: Earth’s climate is warming (NASA 2016)

“Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased” (IPCC the physical science 2013).

97% of Experts Agree  (Huffington Post May 2017)

List of Worldwide Scientific Organizations that Hold the Position That
Climate Change Has Been Caused by Human Action
https://www.opr.ca.gov/s_listoforganizations.php

Consensus on Consensus: 97% of the World’s Climate Scientists Say Humans Are Causing Climate Change

Those 3% of scientific papers that deny climate change? A review found them all flawed (Sept 2017).

NASA Quiz: Global warming

Climate change: Is your opinion informed by science? Take our quiz!  (Christian Science Monitor)

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Next

Home  Chapter 1 1.   The natural Greenhouse effect
Chapter 2 2.  Global Warming
2.1 Authoritative sources
2.2 The Sun?
2.3 Volcanoes?
2.4 Winter is cold?
2.5 Mitigation and adaptation
 Chapter 3 3. Impacts
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