Brief Summary of the Climate Change Science

Fossil fuels, such as coal, oil and gas, were formed over millions of years from the remains of living organisms buried under high pressure and temperature in sediment and water. They are one of the most energy-rich sources we know of today because they contain high concentrations of biological carbon.

In the relatively short period of time since the launch of the Industrial Revolution, fossil fuels have been consumed at an alarming rate by humans for energy use, particularly in comparison to the millions of years it took for the fuels to accumulate. The corresponding amounts of carbon dioxide (CO2) and other gasses emitted as a byproduct of this consumption have been impressive. The volume of these greenhouse gasses (GHG) (called so due to their heat-trapping qualities) has been rising, and is changing our planet’s environment.

The current scientific consensus is the following:

  1. Warming of the climate system is happening and is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global sea levels.
  2. Global GHG emissions have significantly increased since pre-industrial times, with an increase of 70% between 1970 and 2004. The atmospheric concentrations of CO2 and methane (CH4) in 2005 exceed by far the natural range over the last 650,000 years.
  3. Global increases in CO2 concentrations are due primarily to fossil fuel use, with land-use change providing another significant but smaller contribution.Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (human-made) GHG concentrations.

Severe winter of 2015The only remaining debate is about the speed and the damaging impact of climate change as it unravels. Many models have predicted accurately the increase in the number and intensity of extreme weather events, such as droughts, floods, and storms. It now appears that these models have been conservative in their predictions, as evidenced by the increased frequency of extreme weather events and the dramatic melting of the two polar ice sheets. According to the National Oceanic and Atmospheric Administration (NOAA), 2000-2010 was the warmest decade on record. In 2011, weather stations throughout the U.S. identified 121 locations experiencing the wettest year on record, 45 experiencing the driest, 17 experiencing the hottest, and 2 experiencing the coldest.

According to the NOAA, 2012 was the hottest on record for the contiguous 48 states and the second-worst in terms of extreme weather events like tornadoes, wildfires and drought. 2012 was also a full degree higher than the now second highest average temperature set in 1998, the biggest jump from one record temperature to another.

In Massachusetts, the threat of climate change affecting daily life is very real. According to the 2007 Northeast Climate Impacts Assessment (NECIA) report, the annual average temperature will rise 4 to 5 degrees Fahrenheit by 2050. The average number of days over 90 degrees will increase from 5-20 to 30-60 days, much like North Carolina’s climate is today. We are, in fact, already beginning to see the effects of climate change.

Since the beginning of human civilization to relatively recently, there were 275 parts per million (ppm) of carbon dioxide in the atmosphere. In 2012 CO2 concentrations reached 393.14 ppm, up from the 2006 level of 381.2 ppm.

The general scientific consensus is that the planet needs to reduce its carbon emissions to no more than 350 ppm for the atmosphere to be able to absorb and recycle the extra carbon in such a way that does not misbalance the delicate equilibrium of our eco-systems.

For a global-scale problem, no one solution would be sufficient. Additionally, in order to address the global climate change challenges and risks, a sustainable approach should be employed that considers all three pillars of sustainability – environment, economy and equity. Worcester has the obligation and the need to contribute to reduction of GHG emissions, but also has to be mindful of the effects on the economy and population equity. Opportunities are abound to turn this problem into a positive driver for Worcester sustainable development.

The City’s Climate Action Plan will help to set that course.

Learn more about Climate Change

  • NOAA is a source of timely and authoritative scientific data and information about climate with a goal of promoting public understanding of climate science and climate-related events, and to make data products and services easy to access and use.

  • NASA - Global Climate Change: Vital Signs of the Planet's mission is to provide the public with accurate and timely news and information about Earth’s changing climate, along with current data and visualizations.


  • “Climate Change 2007: Synthesis Report. An Assessment of the Intergovernmental Panel on Climate Change.” and “IPCC, 2007: Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

  • Definition of climate change in IPCC usage refers to a change in the state of the climate that can be identified (e.g. using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer. It refers to any change in climate over time, whether due to natural variability or as a result of human activity. Source: “Climate Change 2007: Synthesis Report. An Assessment of the Intergovernmental Panel on Climate Change.”

  • When dealing with very large and complex systems on a planetary scale, it is close to impossible to draw a conclusion that two events are 100% related/correlated, therefore - “very likely” is a statistical and scientific shorthand for certainty.