Update of latest Global Warming information
This will be a short note this week because I am involved in the 43rd NORWESCON Science Fictions Convention in Seattle. I will present brief but interesting summaries of what I read this week and vow to give you a more detailed blog next week. One topic I have been focused on are ways to cool the Earth despite the carbon dioxide buildup. This would give us time to develop cost effective alternatives for fossil fuels and allow third world countries to raise their standards of living to first world levels without major disruption caused by global warming restrictions.
Science Panel Says US Must Consider Air Cooling Technology As Climate Back-Up
The AP (3/25) reports that the US “must seriously consider the idea of tinkering with the atmosphere to cool a warming Earth and accelerate research into how and whether humanity should hack the planet, the National Academy of Sciences said Thursday.” The report “doesn’t recommend carrying out solar geoengineering to bounce heat back to space,” at least not yet. An emergency plan “needs to be explored, the report says, because climate change-driven extreme weather has worsened since the last time the academy looked at the highly-charged issue in 2015.” That requires coordinated research “into whether air-tinkering technology would work, its potentially dangerous side effects, its ethics and the potential for political fall-out.” The report “looks at three possible ways to cool the air: Putting heat-reflecting particles in the stratosphere, changing the brightness of ocean clouds and thinning high clouds.”
Is Current Warming Natural?
In Earth’s history before the Industrial Revolution, Earth’s climate changed due to natural causes not related to human activity. Most often, global climate has changed because of variations in sunlight. Tiny wobbles in Earth’s orbit altered when and where sunlight falls on Earth’s surface. Variations in the Sun itself have alternately increased and decreased the amount of solar energy reaching Earth. Volcanic eruptions have generated particles that reflect sunlight, brightening the planet and cooling the climate. Volcanic activity has also, in the deep past, increased greenhouse gases over millions of years, contributing to episodes of global warming.
These natural causes are still in play today, but their influence is too small, or they occur too slowly to explain the rapid warming seen in recent decades. We know this because scientists closely monitor the natural and human activities that influence climate with a fleet of satellites and surface instruments.
NASA satellites record a host of vital signs including atmospheric aerosols (particles from both natural sources and human activities, such as factories, fires, deserts, and erupting volcanoes), atmospheric gases (including greenhouse gases), energy radiated from Earth’s surface and the Sun, ocean surface temperature changes, global sea level, the extent of ice sheets, glaciers and sea ice, plant growth, rainfall, cloud structure, and more.
On the ground, many agencies and nations support networks of weather and climate-monitoring stations that maintain temperature, rainfall, and snow depth records, and buoys that measure surface water and deep ocean temperatures. Taken together, these measurements provide an ever-improving record of both natural events and human activity for the past 150 years. This data is summarized in figure 1 below.
Figure 1 – Natural Influences on Global Warming
Scientists integrate these measurements into climate models to recreate temperatures recorded over the past 150 years. Climate model simulations that consider only natural solar variability and volcanic aerosols since 1750—omitting observed increases in greenhouse gases—are able to fit the observations of global temperatures only up until about 1950. After that point, the decadal trend in global surface warming cannot be explained without including the contribution of the greenhouse gases added by humans.
Though people have had the largest impact on our climate since 1950, natural changes to Earth’s climate have also occurred in recent times. For example, two major volcanic eruptions, El Chichon in 1982 and Pinatubo in 1991, pumped sulfur dioxide gas high into the atmosphere. The gas was converted into tiny particles that lingered for more than a year, reflecting sunlight and shading Earth’s surface, but temperatures across the globe only dipped slightly for two to three years.
Although volcanoes are active around the world and continue to emit carbon dioxide as they did in the past, the amount of carbon dioxide they release is extremely small compared to human emissions. On average, volcanoes emit between 130 and 230 million tonnes of carbon dioxide per year. By burning fossil fuels, people release in excess of 100 times more, about 26 billion tonnes of carbon dioxide, into the atmosphere every year (as of 2005). As a result, human activity overshadows any contribution volcanoes may have made to recent global warming.
Changes in the brightness of the Sun can influence the climate from decade to decade, but an increase in solar output falls short as an explanation for recent warming. NASA satellites have been measuring the Sun’s output since 1978. The total energy the Sun radiates varies over an 11-year cycle. During solar maxima, solar energy is approximately 0.1 percent higher on average than it is during solar minima.
Figure 2 – Solar Maximum (right) and Solar Minimum (left)
Each cycle exhibits subtle differences in intensity and duration. As of early 2010, the solar brightness since 2005 has been slightly lower, not higher, than it was during the previous 11-year minimum in solar activity, which occurred in the late 1990s. This implies that the Sun’s impact between 2005 and 2010 might have been to slightly decrease the warming that greenhouse emissions alone would have caused.
Figure 3 – Solar Radiance by Year
Scientists theorize that there may be a multi-decadal trend in solar output, though if one exists, it has not been observed as yet. Even if the Sun were getting brighter, however, the pattern of warming observed on Earth since 1950 does not match the type of warming the Sun alone would cause. When the Sun’s energy is at its peak (solar maxima), temperatures in both the lower atmosphere (troposphere) and the upper atmosphere (stratosphere) become warmer. Instead, observations show the pattern expected from greenhouse gas effects: Earth’s surface and troposphere have warmed, but the stratosphere has cooled.
Figure 4 – Atmospheric Heating and Cooling by Year
The stratosphere gets warmer during solar maxima because the ozone layer absorbs ultraviolet light; more ultraviolet light during solar maxima means warmer temperatures. Ozone depletion explains the biggest part of the cooling of the stratosphere over recent decades, but it can’t account for all of it. Increased concentrations of carbon dioxide in the troposphere and stratosphere together contribute to cooling in the stratosphere.
How Much More Will Earth Warm?
To further explore the causes and effects of global warming and to predict future warming, scientists build climate models—computer simulations of the climate system. Climate models are designed to simulate the responses and interactions of the oceans and atmosphere, and to account for changes to the land surface, both natural and human-induced. They comply with fundamental laws of physics—conservation of energy, mass, and momentum—and account for dozens of factors that influence Earth’s climate.
Though the models are complicated, rigorous tests with real-world data hone them into powerful tools that allow scientists to explore our understanding of climate in ways not otherwise possible. By experimenting with the models—removing greenhouse gases emitted by the burning of fossil fuels or changing the intensity of the Sun to see how each influences the climate—scientists use the models to better understand Earth’s current climate and to predict future climate.
The models predict that as the world consumes ever more fossil fuel, greenhouse gas concentrations will continue to rise, and Earth’s average surface temperature will rise with them. Based on a range of plausible emission scenarios, average surface temperatures could rise between 2°C and 6°C by the end of the 21st century.
Figure 5 – IPCC Global Warming Scenarios (©2007 IPCC WG1 AR-4.)
Model simulations by the Intergovernmental Panel on Climate Change estimate that Earth will warm between two and six degrees Celsius over the next century, depending on how fast carbon dioxide emissions grow. Scenarios that assume that people will burn more and more fossil fuel provide the estimates in the top end of the temperature range, while scenarios that assume that greenhouse gas emissions will grow slowly give lower temperature predictions. The orange line provides an estimate of global temperatures if greenhouse gases stayed at year 2000 levels. Overall the picture doesn’t look good, but I will finish this story next week.
Thanks for reading.
Dana Andrews
https://earthobservatory.nasa.gov/features/GlobalWarming
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