February 8, 2018 – I am a retired government biologist living in a rural California community that generally votes Republican.   Recently a local club asked me to give a talk, about climate change science. I resisted the request because I realized I didn’t know as much as I should about climate change and, frankly it would be a lot of work.   Also, like our country, my community is divided right down the middle on this issue with roughly only half the population thinking humans are changing the earth’s climate. 1  I had my own unanswered questions however, so I took this opportunity to explore the science.  I organized my research and talk around 5 questions:  Is climate change happening? Are humans the cause?  Do the experts agree?  Is climate change dangerous?  And, Can we fix it?  Here is what I found and what I told my audience of 114.

I found there were multiple lines of evidence that provide a compelling picture of the climate change upon us.   Instrumental records show global mean temperatures are rising in the air and the ocean.  Sixteen of the warmest years in our 136 year record occurred in the 21st century. 2   When we look back further at the earth’s temperature record through proxies like Oxygen18, we can see they are also the warmest 16 years in the last 10 centuries. 2 Both land and sea ice are melting at both poles3 and our 122 Sierra Nevada glaciers could be gone in 50 years4. Animals and plants are shifting their ranges poleward and upward in altitude in our mountains.5 Some, alpine animals like the American Pika have disappeared from my local mountains due to rising summer temperatures.6 The onset of spring is earlier each decade and fall comes later.7  Snowpack in the Sierra Nevada melts 3 weeks earlier than in 1948 when the California water project was still just a dream.8  Sea level has risen 8 inches in the last century, has doubled since 2010 and is tracking the highest projections of scientific models.9 The evidence is strong.  The Earth’s climate has changed.

While climate has changed throughout the history of the planet, this time it looks like humans are the culprits.  The pre-history causes of climate change initiation, orbital wobble and tilt, volcanism, and solar output are all in phase now to make the earth cooler not warmer.10 These climate change causes also acted in the past on the scale of millennia, not decades.  When warming the planet they acted in ways to start feedback loops that increased carbon dioxide and methane concentrations in the atmosphere, which ultimately warmed the planet much more. We know from bubbles in 400,000 year old ice from dated cores in the Antarctic and from sediment cores in ancient ocean sediments that an atmospheric carbon dioxide increase foretells a global warming.2 The concentration of carbon dioxide is now over 400 ppm, 40% higher than in 1750.2 This is a concentration higher than any in the last 3 million years due to the burning of fossil fuel.  When carbon dioxide was last this high sea level was 20 feet higher and the Greenland Ice sheet was greatly diminished if not gone entirely.11   It may take some time for glaciers to equilibrate but the melting has begun. The sea is rising.   The Arctic is warming at twice the rate as the global average.12 When poles warm faster than the equator it has in the past been an indicator of greenhouse gas forced warming.  It also alters and weakens the jet steam. The evidence strongly points to human induced climate change.

A majority of Americans, and most of my community, think scientists disagree about whether humans are changing the earth’s climate.   The experts, however, very much do agree. 13   Nearly 200 global scientific organizations, the national science academies of 80 countries, 18 American Scientific Societies agree and over 12,000 scientific papers provide supporting evidence that human activities are rapidly changing the climate.

Scientists also agree the three most dangerous consequences of climate change to be inexorable and irreversible sea level rise, increased intensity and frequency of extreme events and an acceleration of ongoing mass extinctions.  Sea level rise is currently tracking the upper bounds of the IPCC projection.  It will be significant, persistent for centuries, and will adversely affect a billion people directly.  A jet stream weakened by a more rapidly warming arctic is increasing the frequency and persistence of extreme events like floods, tropical cyclones, freezes and droughts.14 Billion-dollar weather related catastrophes used to be rare but the average frequency has dramatically increased since 1980, and 2017 was the costliest year yet.15 Other life on earth also faces a grim climate changed future with massive ecosystem shifts predicted.  Extinction rates, already high in the industrial era, are projected to increase with drowned wetlands, expanded desertification, drought, disrupted seasons and migrations, the loss of coral reefs and the acidification of the ocean.16

At our current global carbon emission rates, which have continued to rise not fall, we likely have no more than 20 years to act to keep the climate under 2 degrees warming,17 an increase the Paris Accord acknowledges may not be sufficient to avert dangerous consequences.  The good news is that mitigating climate change by changing the carbon balance can be done by many efforts by many people, not just governments.  These changes are not just about energy sources but include such things as growing a garden, educating girls in third world  and preserving wetlands and forests.  Paul Hawken in the inspiring book Drawdown18 provides a list of 100 such strategies that can dramatically alter carbon balance by 2050.  Many of the Drawdown strategies have other societal benefits like creating jobs, improving our health, reducing pollution, protecting biodiversity, and fostering equality.   The challenge to humans of a changed climate is very real.   The risks are extraordinary.  The time to plan and to act is increasingly short.  What I came to appreciate in my research is that we all need to educate ourselves about what we can do and what’s more, we may be the last generation that has the chance.


  1. Yale University Climate poll.   http://climatecommunication.yale.edu/visualizations-data/ycom-us-2016/?est=human&type=value&geo=county&id=06017
  2. https://climate.nasa.gov/vital-signs/global-temperature/
  3. https://climate.nasa.gov/vital-signs/land-ice/
  4. H. J. Basagic & A. G. Fountain (2011) Quantifying 20th Century Glacier Change in the Sierra Nevada, California, Arctic, Antarctic, and Alpine Research, 43:3, 317-330
  5. Hitch and Leberg, 2006.  https://thetopoischanging.wordpress.com/2014/05/23/climate-lingo-1-isotherms-were-moving-poleward-baby/
  6. https://ww2.kqed.org/science/2017/08/31/climate-change-spells-extinction-for-pikas-of-lake-tahoe/
  7. http://www.climatecentral.org/blogs/tracking-springs-early-onset


  1. https://www.skepticalscience.com/sea-level-rise-predictions.htm

10 https://www.bloomberg.com/graphics/2015-whats-warming-the-world/

11  http://science.sciencemag.org/content/349/6244/aaa4019

12 https://www.nature.com/articles/ngeo2234

  1. https://www.skepticalscience.com/global-warming-scientific-consensus.htm
  2. https://www.npr.org/sections/thetwo-way/2014/02/16/277911739/warming-arctic-may-be-causing-jet-stream-to-lose-its-way

15 https://www.ncdc.noaa.gov/billions/

  1. https://climate.nasa.gov/news/645/climate-change-may-bring-big-ecosystem-changes/

17 https://www.carbonbrief.org/analysis-only-five-years-left-before-one-point-five-c-budget-is-blown

  1. http://www.drawdown.org/

About the Author:  Steven Schwarzbach has a PhD in Ecology from University of California Davis.  He retired as the Director of the USGS Western Ecological Research Center in 2014.  He lives on 5 acres in the foothills of the Sierra Nevada where he raises chickens, grows a garden and skis the mountains when there is adequate snowfall.