Category Archives: climate change

U.S. National Academy of Sciences: Guidance on Climate Change

Today marks the 150thanniversary of the creation of the U.S. National Academy of Sciences.  It may seem impossible in today’s gridlocked environment, but in 1863, President Lincoln proposed it, and Congress passed the law creating the National Academy (NAS) in a matter of days. Its mission was to advise our government about matters of science and engineering that were beyond the training of politicians. And the Industrial Revolution was expanding exponentially the number and complexity of such issues.

Today, the NAS numbers more than 2,000 elected members from among the country’s most distinguished researchers. These are private citizens who share their expertise with the nation without compensation. It is, without question, the most authoritative voice in the nation on matters of science, engineering, medicine and technology.


NAS climate guidance: Free download
Our politicians, meanwhile, are deadlocked today over the issue of climate change: Is it real? What’s causing it? How severe are its consequences? We hope they’re aware that the NAS has repeatedly weighed in on the subject, and has provided some very accessible guidance. The most useful of these, in our judgment, is a 36-page downloadable booklet titled, Climate Change: Evidence, Impacts & Choices. In the following paragraphs, we summarize this short work with a still-shorter outline of key messages from America’s best climate scientists.
  1. Evidence for Human-Caused Climate Change
    1. How do we know that Earth has warmed?  Widespread measurements of temperature around the world began around 1880. These data have steadily improved and, today, temperatures are recorded in many thousands of locations on the land, over the oceans, and from satellites, ocean sensors and weather balloons. These analyses all show that Earth’s average surface temperature has increased by more than 1.4°F (0.8°C) over the past 100 years, with much of this increase taking place over the past 35 years. 1.4°F is like the difference between the average temperature in Washington, DC and Charleston, SC.
    2. How do we know that greenhouse gases lead to warming?  In 1824, French physicist Joseph Fourier was the first to discover the greenhouse effect. In the 1850s, Irish-born physicist John Tyndall demonstrated the greenhouse effect as scientific fact. In 1896, Swedish scientist Svante Arrhenius calculated the warming power of excess CO2, predicting that if human activities increased CO2 levels, climate warming would result. Much research has built on these classics, but they are no longer in doubt.
    3. How do we know that humans are causing greenhouse gases to increase? CO2 is produced and consumed in many natural processes that are part of the carbon cycle. However, once humans began digging up long-buried forms of carbon such as coal and oil and burning them for energy, additional CO2 began to be released into the atmosphere much more rapidly than in the natural carbon cycle. Other human activities, such as cement production and deforestation also add CO2 to the atmosphere. Today, atmospheric CO2 concentrations exceed 390 parts per million—nearly 40% higher than preindustrial levels, and, according to ice core data, higher than at any point in the past 800,000 years.
    4. How much are human activities heating Earth? There are several well-known human impacts on climate: greenhouse gas emissions are the most familiar; emissions from burning fuels also produce small atmospheric particles called aerosols, which have a slight cooling effect; and land-use changes (farming, urban development and deforestation) also have – surprisingly – a slight overall cooling effect. But when these human impacts are taken together, the net climate impact is pushing the earth toward warming.


Ice core data: CO2 and temperature move together
To visualize the extra heat from human climate warming, picture the small Christmas lights that many of us use to decorate our trees or homes over the holidays. Imagine four of them burning brightly in a square meter of space – about the area of your shower stall or bathtub bottom. Now, add four of those same lights to every single square meter over the face of the earth and ocean.  This extra heating equals about 50 times the amount of power produced by all the power plants of the world combined, and that heat is added to Earth’s climate system every second of every day.
    1. How do we know the current warming trend isn’t caused by the Sun? Since 1979, we have measured the Sun’s energy from satellites. These records show that the Sun’s output has not shown a net increase during the past 30 years and thus cannot be responsible for the warming during that period. And since the 1950s, weather balloons have measured temperatures in both the lower and upper atmosphere. More intense heat from the Sun would warm all layers; but in fact, the upper layers have cooled, and the lower layers have warmed. Satellite and weather balloon measurements have been closely scrutinized, and both show a warming trend in the lower layer of the atmosphere and a cooling trend in the upper layer. The Sun is not the cause of today’s global warming.
    2. How do we know the current warming trend isn’t caused by natural cycles? Many natural factors affect the Earth’s climate, including volcanic activity, El Nino and La Nina cycles, and small changes in our orbit around the Sun. Scientists have modeled the impact of these natural impacts on climate over the last 50 years, and have concluded that their combined effects have been largely neutral to slightly cooling. There is a more than 90% chance that most of the observed global warming trend over the past 50 to 60 years can be attributed to emissions from the burning of fossil fuels and other human activities.
    3. What other climate changes and impacts have been observed? Global warming is not uniform all over the globe, and its effects vary from place to place. Major observed impacts include:
                                                               i.      The strongest warming has occurred over land, and most significantly in the Arctic.
                                                             ii.      Heat waves and record high temperatures have increased across most regions of the world.
                                                            iii.      Arctic sea ice cover has decreased 10% per decade, and continues to set new lows.
                                                           iv.      Many of the world’s glaciers and ice sheets are melting.
                                                             v.      Sea levels are rising due to thermal expansion as oceans warm, and because of ice melt.
                                                           vi.      More CO2 in the atmosphere reacts with sea water to form acids. Ocean acidity has increased 30% since preindustrial times, and this is radically altering marine ecosystems.
                                                          vii.      With more water vapor in warmer air, storms are becoming more intense. The Northeast region of the U.S. has seen a 54% increase in intensity of storms over the last century.
                                                        viii.      Species have shifted their ranges pole-ward to adjust to warming climates, or have become endangered due to immobility.
                                                           ix.      Plant and animal behaviors, such as breeding, blooming and migration occur on average 5 days earlier per decade. This affects the timing and severity of insects, disease outbreaks and other disturbances.
  1. Warming,  Climate Changes, and Impacts in the 21st Century and Beyond
    1. How will temperatures be affected?  By the end of the century, the center of the United States is expected to experience 60 to 90 additional days per year in which the heat index is more than 100°F. The ratio of new record high temperatures to record low temperatures currently stands at 2 to 1. But that ratio is projected to increase to 20 to 1 by mid-century and 50 to 1 by the end of the century.
    2. How is precipitation expected to change? Globally, dry areas are expected to get even drier and wet areas even wetter. Some notable details:
                                                               i.      The subtropics, where most of the world’s deserts are concentrated, are likely to see 5-10% reductions in precipitation for each degree of global warming. Mexico and the American Southwest are likely to get much drier.
                                                             ii.      Polar and temperate regions are expected to see increased precipitation, especially during winter.
                                                            iii.      Extreme rainstorms are likely to intensify by 5-10% for each 1°C (1.8°F) of global warming, resulting in more intense flooding, even in regions that will be drier.
                                                           iv.      Wildfires will become more intense and widespread. For every degree of warming, the forest area burned is expected to increase by a factor of 2x to 4x.
    1. How will sea ice and snow be affected? In the Arctic, sea ice will decline 25% for each 1°C (1.8°F) in global warming this century. In the Antarctic, sea ice is expanding due to the stratospheric “ozone hole” which developed because of the use of ozone-depleting chemicals; this effect is expected to wane as ozone returns to normal levels by later this century. In many areas of the globe, snow cover is expected to diminish, with snowpack building later in the cold season and melting earlier in the spring. Each 1°C (1.8°F) of local warming may lead to an average 20% reduction in local snowpack in the western United States; reduced snowpack will restrict summer drinking water supply and hydropower production.
    2. How will coastlines be affected?  Sea-level rise is projected to continue for centuries in response to human- caused increases in greenhouse gases, with an estimated 20-39 inches of mean sea-level rise by 2100, and more beyond. However, there is evidence that sea level rise could be much greater, due to unexpectedly rapid melting from glaciers and ice sheets. If sea levels rise by 39 inches this century, many parts of the U.S. coastline will be impacted (see map below). In any event, global “hotspots,” including the Mississippi, Ganges and Mekong River deltas will be seriously affected.
    3. How will ecosystems be affected? Species are adapted to specific climatic conditions in their ecosystems. As the climate changes, many species will be forced to migrate. But this threatens many species with limited mobility. Special stress is being placed on cold-adapted species on mountain tops and at high latitudes, which cannot move higher or further pole-ward. Shifts in the timing of the seasons and life-cycle events such as blooming, breeding, and hatching are causing mismatches between species, disrupting patterns of feeding, pollination, and other key aspects of food webs.
Large losses to American cities from 39” sea rise (pink shading)
In the ocean, warmer surface waters are mixing less with cooler, deeper waters, separating near-surface marine life from the nutrients below and ultimately reducing the amount of phytoplankton, which forms the base of the ocean food web. Ocean acidification, brought on as the oceans take in more of the excess CO2 will threaten many species over time, especially mollusks and coral reefs.  Ocean acidification will continue to worsen if CO2 emissions continue unabated in the decades ahead.
    1. How will agriculture and food production be affected?  Warmer weather and increased CO2 do not necessarily mean a decline in food production. However, temperature increases above 1°C (1.8°F) will reduce yields in almost all of the world’s staple foods, a result of water stress and temperature peaks. Local results will also vary, with a projected 40% yield decrease in a broad cross section of California crops by 2050. Growers in prosperous areas may be able to adapt to some climate threats. However, adaptation may be less effective where local warming exceeds 2°C (3.6°F), and will be limited in many poorer countries and the tropics, where crop yields are restricted principally by moisture.
We are glad that for the last 150 years, so many of America’s brightest researchers have been willing to donate their expertise for the sake of our country and its leadership. President Lincoln had the foresight to see the value of such an enterprise. Let us pray that today’s leaders will show similar wisdom.
“Where there is no guidance, a people falls, but in an abundance of counselors there is safety” (Proverbs 11:14).
Thanks for reading, and may God bless you.
J. Elwood
Further Resources

Cliff Notes for the U.N. IPCC 2007 Report

In 2007, the Intergovernmental Panel on Climate Change won the Nobel Peace Prize for its efforts “to build up and disseminate greater knowledge about man-made climate change.” Some people loved their work. Others hated it. But the Nobel Committee decided that their work deserved extraordinary recognition.

Now, the IPCC is preparing to issue its 5th assessment later this year, and some of its drafts have already been circulating on the web. We can surely expect fireworks. Many still consider climate science to be a “massive hoax,” and they won’t take kindly to a synthesis of global science that provides more certainty regarding the trends in climate disruptions.
But before the new edition comes out, it might be good to know what the old one actually said. Of course, you don’t actually want to read it yourself. The thing consists of four volumes, covering basic science, vulnerabilities, mitigation, and a synthesis report. It’s so cumbersome that most commentators settle for reading only a Summary for Policymakers.
But it can be read, and we’ve done so. We thought that it might be a service to summarize – in layman’s terms – the Physical Science Basis Report. This tells us the state of basic climate science six years ago. A lot more is known today, but here’s a readable summary of what was known back then. We paraphrase most everything, but our account is an honest every-man’s rendering of largely impenetrable scientific language.
1. Greenhouse gases are increasing:  Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities and now far exceed pre-industrial values.
  • Highest recorded carbon levels:  Carbon dioxide is the most important anthropogenic greenhouse gas. The global concentration of carbon dioxide has increased from a pre-industrial value of about 280 ppm to 379 ppm in 2005, and now exceeds by far the natural range over the last 650,000 years. (Note: CO2 is now at 395.55 ppm.)
  • Faster growth in carbon: The annual carbon dioxide concentration growth rate was larger during the last 10 years than it has been since the beginning of continuous direct atmospheric measurements.
  • It comes from burning coal and oil:  The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use.
2.  Warming of the climate system is unequivocal, as is now evident from observations of increases in global air and ocean temperatures, widespread melting of snow and ice, and rising global average sea levels.
  • These are the hottest years:  Eleven of the last twelve years (1995–2006) rank among the 12 warmest years on record (since 1850). (Note: The 6 years since then have all been hotter than every year before 1997, and include the #1, #5, and #6 hottest on record.)
  • The pace of warming is accelerating:  The linear warming trend over the last 50 years (0.13°C per decade) is nearly twice that for the last 100 years.
  • The oceans are getting hotter:  Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3,000 meters and that the ocean has been absorbing more than 80% of the heat added to the climate system. Such warming causes seawater to expand, contributing to sea level rise.
  • Glaciers are melting: Mountain glaciers and snow cover have declined on average in both hemispheres. Widespread decreases in glaciers and ice caps have contributed to sea level rise.
  • Polar ice is melting:  Losses from the ice sheets of Greenland and Antarctica have very likely contributed to sea level rise from 1993 to 2003.
  • Seas are rising:  Global average sea level rose faster in the 20th century than in the 19th century; faster yet in 1961-2003; and nearly double that rate during 1993-2003.  Everything is accelerating.
3.  Global warming is affecting the Polar Regions and the tropics most significantly.
  • The Arctic is melting:  Average Arctic temperatures increased at almost twice the global average rate in the past 100 years.  Since 1978, annual average Arctic sea ice coverage has shrunk by 2.7% per decade, with larger decreases in summer of 7.4% per decade.
  • The permafrost is thawing:  Temperatures at the top of the permafrost layer have increased since the 1980s in the Arctic by 3°C. The maximum area covered by seasonally frozen ground has decreased by about 7% in the Northern Hemisphere since 1900.
  • It’s dryer in Africa, and wetter in the Americas:  Significantly increased precipitation has been observed in eastern parts of North and South America, northern Europe and northern and central Asia. Drying has been observed in the African Sahel, the Mediterranean, southern Africa and parts of southern Asia.
  • Drought for the tropics:  More intense and longer droughts have been observed over wider areas since the 1970s, particularly in the tropics and subtropics. Increased drying linked with higher temperatures and decreased precipitation has contributed to increases in drought.
  • More intense flooding storms:  The frequency of heavy precipitation events has increased over most land areas, consistent with warming and observed increases of atmospheric water vapor.
  • Stronger hurricanes:  There is observational evidence for an increase in intense tropical cyclone activity in the North Atlantic since 1970, correlated with increases of tropical sea surface temperatures.

4.  The warmth of the last half century is unusual in at least the previous 1,300 years.
  • This doesn’t happen regularly:  Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years.
  • When it does, oceans rise significantly: Looking way back, global average sea level in the last interglacial period (about 125,000 years ago) was likely 4 to 6 meters higher than during the 20th century. Ice core data indicate that average polar temperatures at that time were 3°C to 5°C higher than present. 
5.  We can no longer say “It’s not our fault.”  Most of the observed increase in global average temperatures since the mid-20th century is very likely due to increases in human-caused greenhouse gases. 
  • Natural cycles have actually reduced warming: Increases in greenhouse gas concentrations alone would have caused more warming than observed because volcanic and human-caused aerosols have offset some warming that would otherwise have taken place.
  • Nature hasn’t caused these events:  It is extremely unlikely that global climate change of the past 50 years can be explained without external factors, and very likely that it is not due to known natural causes alone.
6.  For the next two decades, a warming of about 0.2°C per decade is projected. Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected.
  • With more greenhouse gases, the Earth must get hotter before reaching equilibrium:  Warming is likely to be in the range 2°C to 4.5°C with a best estimate of about 3°C, and is very unlikely to be less than 1.5°C.
  • Actual observed warming confirms the IPCC’s initial warnings:  In the first report in 1990, projections were for global average temperature increases between about 0.15°C and 0.3°C per decade for 1990 to 2005. This can now be compared with observed values of about 0.2°C per decade.
7.  Current trends spell accelerated warming:  Continued greenhouse gas emissions at or above current rates will cause further warming and cause many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.
  • It will be at least 1.8°C hotter this century: Best estimates for surface air warming in the 21st century is 1.8°C and the best estimate for the high scenario is 4.0°C.
  • A hotter Earth will mean even more carbon emissions:  Warming tends to reduce land and ocean uptake of atmospheric carbon dioxide, increasing the fraction of carbon emissions that remain in the atmosphere.
  • Sea levels will rise further:  Projections of global average sea level rise at the end of the 21st century are 0.3 to 0.6 meters, with most of the models projecting 0.2-.0.3 meters of sea level rise, excluding the impact of increases in polar ice flow. (Note: Most projections since this report point to much higher levels of sea level rise.)
  • It could be much worse:  Models used so far do not include uncertainties in climate-carbon cycle feedback nor do they include the full effects of changes in polar ice flow, because published research was lacking at the time.
  • White, reflective snow and ice will be replaced by dark land and oceans:  Snow cover is projected to decrease. Widespread increases in thaw depth are projected over most permafrost regions.  Sea ice is projected to shrink in both the Arctic and Antarctic. In some projections, Arctic late-summer sea ice disappears almost entirely.
  • More extreme weather ahead:  It is very likely that hot extremes, heat waves and heavy precipitation events will continue to become more frequent.  It is likely that future tropical cyclones (typhoons and hurricanes) will become more intense.
  • It will be dryer in the tropics, and wetter nearer the poles:  Increases in the amount of precipitation are very likely in high latitudes, while decreases are likely in most subtropical land regions.
8.  No quick fixes:  Human-caused warming and sea level rise will continue for centuries due to the time scales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized.
  • Big cuts in carbon are necessary just to stabilize:  Based on current understanding of climate-carbon cycle feedback, studies suggest that to stabilize at 450 ppm carbon dioxide could require that cumulative emissions over the 21stcentury be reduced by 27% from 2006 levels.
  • Sea levels will keep rising regardless of what we do:  If greenhouse gases were to be stabilized at 2006 levels, thermal expansion alone would lead to 0.3 to 0.8 m of sea level rise by 2300 (relative to 1980–1999).  Thermal expansion would continue for many centuries, due to the time required to transport heat into the deep ocean.  Melting of Greenland Ice is projected to continue to contribute to sea level rise after 2100, and could result in a rise in sea levels of about 7 meters.
  • This struggle will go on for centuries:  Both past and future human-caused carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium, due to the time scales required for removal of this gas from the atmosphere.
J. Elwood

The Rising Seas: A Peek Inside the Scientific Debate

The issue of rising sea levels came back into national focus last week when one of our presidential contenders used the matter as a laugh line before a throng of cheering supporters.  He recalled that his opponent had vowed to take action to stem rising sea levels, pausing with a perplexed grin, as the laughter grew to a raucous crescendo. Obviously, many Americans aren’t very worried.
The event rekindled my interest in the topic. Two years ago, I read a fascinating book by Duke University’s Orrin Pilkey: The Rising Sea. Pilkey, seen by many as the dean of America’s coastal scientists, urged city planners in 2009 to plan on seven feet of sea level rise on U.S. coasts by the end of the century.  That would essentially eliminate beachfront development anywhere in the East.
But with the passage of several years, I figured there must be plenty of new material. There was. I settled on a $3.00 eBook offering by Daniel Grossman, a National Geographic editor, titled Deep Water: As Polar IceMelts, Scientists Debate How High Our Oceans Will Rise
I liked “Deep Water.” In a few short hours of reading, Grossman guides the reader through the messy business of real scientific research: geologists and geochemists negotiating the challenges of hungry Hudson Bay polar bears, temperamental Australian rental vans and competing scientific specialties (and egos) to get to the bottom of genuine controversies.
In this case, the controversy was whether current levels of global warming should be expected to raise global sea levels by 62 feet, or perhaps only 31 feet, the consensus view supported by most geochemists.  The search for the answer takes the reader to Southwest Australia, Bermuda, the Bahamas, Boston and New York.
In a nutshell, much is already understood about ice ages and interglacial warm periods in the distant past: how warm or cold they were; how much CO2 was in the atmosphere at the time; and the advance and retreat of ice sheets – among many other features. Two warm periods, however, deserve special attention: the one preceding the last ice age 125,000 years ago (clumsily named “Stage 5e”), and one dated about 400,000 years ago (“Stage 11”). These two “interglacials” are thought to be the hottest times on earth for several millions of years – but only 1 degree Fahrenheit hotter than the world is today.
Scientists generally agree that much of both the Greenland and West Antarctic ice sheets melted during these two stages, raising global sea levels about 30 feet above where they are today. But geologists have recently found unmistakable signs of ancient fossil seashores dating back to Stage 11 in the geologically-stable regions of the Bahamas and Bermuda. And here’s the problem: those features are more than 60 feet above today’s sea levels.
Did sea levels rise more than 60 feet in these warm stages? If so, the implications are serious: The massive East Antarctic ice sheet had to have been aroused, in addition to the somewhat smaller Greenland and West Antarctic sheets. And while Stages 5e and 11 were slightly warmer than today, our era will bypass them both during this generation, with no end to heating in sight, due to our much higher levels of atmospheric greenhouse gases, and continued inaction on curbing emissions.
In the end, it looks like 31 feet of additional sea level rise for Stages 5e and 11 is the more probable estimate. (Find out why for yourself!) But the journey is well worth the read, and I recommend that you follow the thread for yourself.
I should add that it’s not just idle curiosity driving these researchers. If we manage to stabilize the climate by significantly reducing greenhouse gases in our lifetime, there’s a good chance that sea levels will again peak at about 31 feet above where they are today. If we don’t, then then it’s more likely that East Antarctica will also get in on the melting. We can only speculate at what that might mean. But even the lower level of 31 feet would inundate 25% of the U.S. population, according to the U.S. Geological Survey.
And at the higher levels? Nobody wants to think about that, not even me.
Thanks for caring about this, and may God bless you.
J. Elwood
More images related to sea level science:
USGS map of new coastline at 30′ rise
Fossil beaches: Wave-cut terraces on geologically-unstable San Clemente, CA