Global Warming/Climate Change is a contentious issue of modern times, but too important of an issue, with implications for everyone on Earth, to ignore and for us to remain uninformed about the scientific evidence and predictions about its consequences for us and the rest of the biosphere. The scientific literature is building and consensus about its reality, as well as the evidence that its major driver is human activity, is growing. Between 1970 and 1990 less than 1,000 scientific articles, books and conference proceedings were published about climate change in English. However, by the end of 2012 there were over 102,000 and the number is dramatically increasing as more and more people are affected and become aware of global warming/climate change. When you include scientific articles from Africa, Asia, Latin America, Europe and Australia, the number is even greater.
The Intergovernmental Panel on Climate Change (IPCC), a major organization founded by the United Nation's World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), has recently released (March 31, 2014) one of the most comprehensive reports and analysis of climate change to date. It also includes some of the most sophisticated, scientific models for predicting future outcomes of Global Warming/Climate change. I've taken it upon myself to read as much of the IPCC report as I humanly can and to write a blog series summarizing and citing its findings to inform you about the current state of science on the issue of Global Warming/Climate Change. It was reviewed by 1729 experts from 84 countries, had 436 contributing authors from 54 countries and over12,000 scientific references were cited. The panel made a conscious effort to have a diverse and fair representation of authors and reviewers, both in terms of gender and national background, to minimize political, religious and cultural biases.
Summary and Citations From Technical Summary of Work Group I of IPCC
"The period 1983–2012 was very likely the warmest 30-year period of the last 800 years and likely the warmest 30-year period of the last 1400 years. Although a certain amount of future climate change is already ‘in the system’ due to the current radiative imbalance caused by historical emissions and the long lifetime of some atmospheric forcing agents (greenhouse gases), societal choices can still have a very large effect on future...climate change.""
There's no doubt that the temperature of the Earth is increasing as it can be and has been directly measured for the past 150 years. Indirectly, the temperature of the Earth and atmospheric gas concentrations can be measured from ice cores and other geological evidence. This record shows a very strong correlation between atmospheric levels of carbon dioxide (CO2), as well as other greenhouse gases to a lesser extent, and the global mean temperature. Because a sharp rise in greenhouse gases and global mean temperature has been observed starting around 1750 and the Industrial Revolution, when the mass combustion of fossil fuels producing copious amounts of carbon dioxide began, it can be inferred with great confidence that humans are causing global warming.
"Concentrations of the atmospheric greenhouse gases (GHGs) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in 2011 exceed the range of concentrations recorded in ice cores during the past 800,000 years."
"Between 1750 and 2011, CO2 emissions from fossil fuel combustion and cement production are estimated from energy and fuel use statistics to have released ~750 trillion pounds of carbon. In 2002–2011, average fossil fuel and cement manufacturing emissions were ~16.6 trillion pounds of carbon per year, with an average growth rate of 3.2% per year. This rate of increase of fossil fuel emissions is higher than during the 1990s (1.0% per year). In 2011, fossil fuel emissions released ~19 trillion pounds of carbon. Between 1750 and 2011, land use change (mainly deforestation), derived from land cover data and modelling, is estimated to have released ~360 trillion pounds of carbon. Land use change emissions between 2002 and 2011 are dominated by tropical deforestation, and are estimated at 1.8 trillion pounds of carbon per year, with possibly a small decrease from the 1990s due to lower reported forest loss during this decade. This estimate includes gross deforestation emissions of around 6 trillion pounds of carbon per year compensated by around 4 trillion pounds of carbon per year of forest regrowth in some regions, mainly abandoned agricultural land."
"Of the approximately 1.1 quadrillion pounds of carbon released to the atmosphere from fossil fuel and land use emissions from 1750 to 2011, 480 trillion pounds of carbon accumulated in the atmosphere.
"An independent line of evidence for the anthropogenic origin of the observed atmospheric CO2 increase
comes from the observed consistent decrease in atmospheric [and oceanic] oxygen (O2) content."
"The concentration of CH4 has increased by a factor of 2.5 since preindustrial times, from 722 parts per billion in 1750 to 1803 parts per billion in 2011. There is very high confidence that the atmospheric CH4 increase during the Industrial Era is caused by anthropogenic activities. The massive increase in the number of ruminants, the emissions from fossil fuel extraction and use, the expansion of rice paddy agriculture and the emissions from landfills and waste are the dominant anthropogenic CH4 sources. Anthropogenic emissions account for 50 to 65% of total emissions."
"Since pre-industrial times, the concentration of N2O in the atmosphere has increased by a factor of 1.2"
Earth absorbs more solar radiation because of the increased presence of these greenhouse gases and the Earth gets warmer as a result. Interestingly though, "ocean warming dominates that total heating rate, with full ocean depth warming accounting for about 93%, and warming of the upper (0 to 700 m) ocean accounting for about 64%. Melting ice (including Arctic sea ice, ice sheets and glaciers) and warming of the continents each account for 3% of the total. Warming of the atmosphere makes up the remaining 1%...........The majority of this additional heat is in the upper 700 m of the ocean, but there is also warming in the deep and abyssal ocean."
The ocean's ability to absorb heat is perhaps the one factor scientists underestimated when creating models for global warming in the past. The ocean seems to be like a sponge for heat that has slowed the overall process of the warming of the Blue Planet thus far. A kilogram of water and a kilogram of air could absorb the same amount of energy, but the air will increase in temperature far more than water will. What's strange, but kind of cool, is that all the energy the ocean has absorbed hasn't raised its temperature much, but it has made it expand causing the sea level to rise slightly. Remember that temperature is the measure of molecular motion. When an object is hotter the molecules are moving faster and the object expands.
"The ocean has stored about 93% of the increase in energy in the climate system over recent decades, resulting in ocean thermal expansion and hence sea level rise............The associated thermal expansion of the ocean has contributed about 40% of the observed sea level rise since 1970." (Overall, the ocean has been measured to have risen by about 8 inches over the period of 1901–2010.)
It's good for us, on land, that the ocean has absorbed most of the heat because if it hadn't we might've baked by now, but the bad thing is that the extra heat energy in the ocean affects the ocean currents.
"Recent observations have strengthened evidence for variability in major ocean circulation systems on time scales from years to decades. It is very likely that the subtropical gyres in the North Pacific and South Pacific have expanded and strengthened since 1993."
Messing with ocean currents is a bad thing because ocean currents have a major impact on weather over the land. It affects climate and temperature along the coast as well as cloud conditions and precipitation.
"Warming could lead to changes in ocean current patterns that could have drastic impacts on climate the world over. Changing patterns of drought and monsoon as well as temperatures. Could also effect the melting of permafrost which would allow for the decomposition of the organic carbon therein releasing much CO2 (carbon dioxide) and CH4 (methane). [Resulting in the] retreat of the Boreal forest as well as causing shifts in the ranges of many animals and plants, which would exacerbate trends that we're already seeing, possibly leading to extinction of vulnerable species which are not that adaptable nor mobile."
In the most extreme cases it can cause super-powerful storms, like hurricanes, which can lead to great damage and loss of life.
"Over the satellite era, increases in the frequency and intensity of the strongest storms in the North Atlantic are robust."
In addition to causing stronger storms global warming will lead to higher evaporation rates and thus the average global humidity will rise as well as the amount of precipitation; even though there will be more precipitation overall, however, it is predicted to be more sporadic with increased intermittent times of drought. In addition, "changes of average precipitation in a much warmer world will not be uniform, with some regions experiencing increases, and others with decreases or not much change at all." This sporadic precipitation falling with greater intensity and the increased periods of intermittent drought will place a strain on crops and food production.
"High latitudes are very likely to experience greater amounts of precipitation....Many mid-latitude and subtropical arid and semi-arid regions will likely experience less precipitation and many moist mid-latitude regions will likely experience more precipitation by the end of this century."
The warming of the oceans and atmosphere acting in synergy have caused glaciers and the polar ice caps to recede, the extent of permafrost to retreat, as well as a reduction in the amount of snow cover in the Northern Hemisphere during winters.
"there is very high confidence that the Arctic sea ice extent (annual, multi-year and perennial) decreased over the period 1979–2012. The rate of the annual decrease was very likely between 3.5 and 4.1% per decade."
"There is high confidence that the average winter sea ice thickness within the Arctic Basin decreased between 1980 and 2008. The average decrease was likely between 1.3 m and 2.3 m."
It could be possible that the Arctic ice cap will change from perennially covered to seasonally covered in our lifetimes. This would wreak havoc on the animals that call the Arctic ice their home.
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"The available evidence indicates that global warming beyond a threshold would lead to the near-complete loss of the Greenland ice sheet over a millennium or longer, causing a global mean sea level rise of approximately 7 m (~23 feet)."
Even though we are adding a lot of carbon dioxide and other greenhouse gases into the atmosphere, resulting in the warming of the Earth and its oceans, a great proportion of the carbon we've released has ended up in the biosphere (mostly through plants and other photosynthetic organisms), oceans and sediments. These carbon sinks have slowed the rise of carbon dioxide in the atmosphere and thus have slowed the rate of climate change (this is why ecosystem services are so important!)
"The human caused excess of CO2 in the atmosphere is partly removed from the atmosphere by carbon sinks in land ecosystems and in the ocean, currently leaving less than half of the CO2 emissions in the atmosphere. Natural carbon sinks are due to physical, biological and chemical processes acting on different time scales. An excess of atmospheric CO2 supports photosynthetic CO2 fixation by plants that is stored as plant biomass or in the soil. The residence times of stored carbon on land depends on the compartments (plant/soil) and composition of the organic carbon, with time horizons varying from days to centuries. The increased storage in terrestrial ecosystems not affected by land use change is likely to be caused by enhanced photosynthesis at higher CO2 levels and nitrogen deposition, and changes in climate favoring carbon sinks such as longer growing seasons in mid-to-high latitudes."
"An excess of atmospheric CO2 absorbed by land ecosystems gets stored as organic matter in diverse carbon pools, from short-lived (leaves, fine roots) to long-lived (stems, soil carbon)."
"The uptake of anthropogenic CO2 by the ocean is primarily a response to increasing CO2 in the atmosphere. Excess atmospheric CO2 absorbed by the surface ocean or transported to the ocean through aquatic systems (e.g., rivers, groundwaters) gets buried in coastal sediments or transported to deep waters where it is stored for decades to centuries. The deep ocean carbon can dissolve ocean carbonate sediments to store excess CO2 on time scales of centuries to millennia. Within a 1,000 years, the remaining atmospheric fraction of the CO2 emissions will be between 15 and 40%, depending on the amount of carbon released. On geological time scales of 10,000 years or longer, additional CO2 is removed very slowly from the atmosphere by rock weathering, pulling the remaining atmospheric CO2 fraction down to 10 to 25% after 10,000 years." An unfortunate side-effect of the ocean absorbing CO2 is that it acidifies the water (the ocean has seen a 26% increase in acidity over the past 250 years). This is bad because the extra acidity dissolves the coral reefs, which can take thousands of years for the organisms to build, and any marine organisms that make calcium carbonate shells.
In fact, increased CO2 in the atmosphere is predicted to increase the amount of plant biomass on Earth, especially in desert areas through a phenomena called the Carbon Dioxide Fertilization Effect. CO2 is a limiting nutrient in many environments and it reduces the amount of growth in plants, but with an excess of CO2 in the atmosphere from the burning of fossil fuels plants put on more biomass until other nutrients in the soil like nitrogen and phosphorous become limiting to growth. One might think that plants are going to offset global warming by up-taking the excess CO2, but in fact we are producing too much greenhouse gases for plant growth to keep up and offset our activities. Additionally, the accelerated rate of plant growth due to higher atmospheric CO2 levels is bad for soils because it will cause nitrogen and phosphorous depletion which are essential nutrients for building proteins and nucleic acids.
"It is very likely, based on new experimental results and modelling, that nutrient shortage will limit the effect of rising atmospheric CO2 on future land carbon sinks. There is high confidence that low nitrogen availability will limit carbon storage on land even when considering anthropogenic nitrogen deposition. The role of phosphorus limitation is more uncertain."
Some skeptics wonder if other natural forces might be causing global warming other than human activity. They might question whether the sun has increased its energy output or if volcanoes have released more carbon dioxide lately than normal.
It is true that the Earth's climate oscillates over time and that in the past there were periods of higher temperatures with higher atmospheric carbon dioxide levels than modern times.
"During warm intervals of the mid Pliocene (3.3 to 3.0 million years ago), there's medium confidence that global mean temperatures were 1.9°C to 3.6°C warmer than the pre-industrial climate and with carbon dioxide (CO2) levels that were between 350 and 450 ppm (modern times is at about 400 ppm), there is high confidence that the global mean sea level was above present, but by no more than 20m (65 feet)."
"There is very high confidence that the maximum global mean sea level during the last interglacial period (129 to 116,000 years ago) was, for several thousand years, at least 5m (16.25 feet) higher than present and high confidence that it did not exceed 10m (323.5 feet) above present, implying substantial contributions from the Greenland and Antarctic ice sheets. This change in sea level occurred in the context of different orbital forcing and with high-latitude surface temperature, averaged over several thousand years, at least 2°C warmer than present."
"During the Early Eocene (52 to 48 million years ago), atmospheric CO2 concentration exceeded about 1000 ppm and the global mean temperature was 9°C to 14°C higher than for pre-industrial conditions."
It is also true that volcanic eruptions and changes in the sun's solar output have effects on the Earth's climate, but the record is pretty clear that these variables are not driving modern climate change. In truth, volcanoes can often have a cooling effect on the Earth's climate by blocking the sunlight with particulate matter.
"Explosive volcanic eruptions (such as El Chichón in Mexico in 1982 and Mt Pinatubo in the Philippines in 1991) can inject sulphur dioxide into the stratosphere, giving rise to stratospheric aerosol, which persists for several years. Stratospheric aerosol reflects some of the incoming solar radiation and thus gives a negative forcing (negative forcing is the same as global cooling in this context). Large tropical volcanic eruptions have played an important role in driving annual to decadal scale climate change during the Industrial Era owing to their sometimes very large negative RF." This is saying that volcanoes do and have played an important role in climate change over the past 250 years, but the majors effect on climate has been cooling.
"The emissions of CO2 from volcanic eruptions are at least 100 times smaller than anthropogenic emissions, and inconsequential for climate on century time scales."
"Solar forcing is the only known natural forcing acting to warm the climate over the 1951–2010 period but it has increased much less than greenhouse-gas-induced-climate-forcing, and the observed pattern of long-term tropospheric warming and stratospheric cooling is not consistent with the expected response to solar irradiance variations. Considering this evidence together with the assessed contribution of natural forcings to observed trends over this period, it is assessed that the contribution from solar forcing to the observed global warming since 1951 is extremely unlikely to be larger than that from greenhouse-gas-induced-climate-forcing. Because solar forcing has very likely decreased over a period with direct satellite measurements of solar output from 1986 to 2008, there is high confidence that changes in total solar irradiance have not contributed to global warming during that period. However, there is medium confidence that the 11-year cycle of solar variability influences decadal climate fluctuations in some regions through amplifying mechanisms."
"Solar and volcanic forcings are the two dominant natural (as opposed to human-caused) contributors to global climate change during the Industrial Era, but there is strong evidence that excludes solar forcing, volcanoes and internal variability as the strongest drivers of warming since 1950."
CONCLUSION
All this evidence pretty overwhelmingly proves that humans are the major driver of modern climate change/global warming and it is being done mainly through the burning of fossil fuels which produces the major culprit greenhouse gases CO2 (carbon dioxide), CH4 (methane), and NO2.
In the next blog of this series I will summarize the last part of the IPCC report which talks more specifically about the impacts to human societies and the environment as well as recommendations for courses of action by the international community to head off this potentially devastating, impending disaster known as climate change/global warming.
-Seth Commichaux
Source Cited:
Technical Summary of Work Group I of IPCC
http://www.climatechange2013.org/images/report/WG1AR5_TS_FINAL.pdf
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