The Earth's climate has changed throughout history. Just in the last 450,000 years there have been five cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era — and of human civilization. Most of these climate changes are attributed to very small variations in Earth’s orbit that change the amount of solar energy our planet receives. But not in the last 450,000 years has the CO2 level gone over 300 ppm. In 1950 it broke 300, and is now over 400 ppm - hence the hockey stick.

Scientific evidence for warming of the climate system is unequivocal - Intergovernmental Panel on Climate Change

The current warming trend is of particular significance because most of it is extremely likely (greater than 95 percent probability) to be the result of human activity since the mid-20th century and proceeding at a rate that is unprecedented over decades to millennia.

Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate.

The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century. Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases must cause the Earth to warm in response.

Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that the Earth’s climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly ten times faster than the average rate of ice-age-recovery warming.

The evidence for rapid climate change is compelling:

Global temperature rise

The planet's average surface temperature has risen about 2.0 degrees Fahrenheit (1.1 degrees Celsius) since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere. Most of the warming occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001. Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year — from January through September, with the exception of June — were the warmest on record for those respective months.

The oceans have absorbed much of this increased heat, with the top 700 meters (about 2,300 feet) of oceans showing warming of 0.302 degrees Fahrenheit since 1969.


Shrinking ice sheets, glacial retreat and less snow cover

The Greenland ice sheets and the Arctic sea ice and Antarctic ice sheets have decreased in mass. Crystal Serenity was the first Cruise Ship in history to pass through the northwest passage in 2016 - from the north Atlantic, through the Canadian Archipeligo, to northern Alaska, as a result of global warming and less arctic sea ice. Data from NASA's Gravity Recovery and Climate Experiment show Greenland lost 150 to 250 cubic kilometers (36 to 60 cubic miles) of ice per year between 2002 and 2006, while Antarctica lost about 152 cubic kilometers (36 cubic miles) of ice between 2002 and 2005. Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa. Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and that the snow is melting earlier.

Sea Level Rise

Global sea level rose about 8 inches in the last century. The rate in the last two decades of that century, however, is nearly double that of first eight decades.


Extreme events

The number of record high temperature events in the United States has been increasing, while the number of record low temperature events has been decreasing, since 1950. The U.S. has also witnessed increasing numbers of intense rainfall events such as hurricanes, and an increase in drought, wildfires and mudslides.

                                              Hurricane Irma                                                                Hurricane Harvey

In September of 2017 Hurricane Irma had sustained winds of 185 mph for 37 hours, the longest that any hurricane around the world has maintained that intensity. Regarding Atlantic hurricanes, Irma had the second highest wind speed of any hurricane at 185 mph, second only to Hurricane Allen at 190mph in 1980. Irma had the second longest duration as a Category 5 hurricane at 3 days and 3 hours, second only to the Cuba hurricane in 1932 at 3 days 6 hours. Hurricane Harvey stalled over southwest Texas and dumped over 50 inches of rain, the most of any US hurricane and 3rd on the list of Atlantic hurricanes on record since 1900. This is the first time in the history of record keeping that two Category 4 or higher hurricanes have struck the U.S. mainland in the same year, and these hit 8 days apart.  This is an example of an increase in storm intensity and of extreme events.

Ocean Acidification

Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent. This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 2 billion tons per year. Ocean acidification occurs when CO2 is absorbed into the water at a high rate. It reacts with water molecules (H2O) to form carbonic acid (H2CO3). The presence of this acid is what decreases the pH, causing coral reefs to bleach and die, and many other impacts on ocean life.

NASA's conclusion based on science with the evidence as presented above: The heat-trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century. Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases must cause the Earth to warm in response.

Global warming and climate change is the result of increased CO2 levels in the atmosphere, which result in global temperature rise, warming oceans, shrinking ice sheets and glacial retreat, extreme weather events like hurricanes and droughts, and ocean acidification.

As the International Panel on Climate Change, based on science, concludes:
Scientific evidence for warming of the climate system is unequivocal.

As the evidence provided shows, global warming and climate change, the result of increased CO2 levels in the atmosphere primarily from the burning of fossil fuels starting with the industrial revolution, is happening as we speak, it’s real. Here’s one more piece of evidence, recall the graph for the human population over time, let’s compare that to the atmospheric CO2 levels over the past million years:

Over the past million years, the spike in the world population coincides exactly with the spike in CO2 in the atmosphere.  The chances of that happening and being completely unrelated are 1 in a million.  Hopefully as a society we will acknowledge climate change and try to mitigate its effects on the environment and society. Climate change is real, the only questions are, to what degree will it impact humanity? And what will we do about it?


Recall that other form of cancer mentioned at the end of Chapter 17 that started as particular companies (the cells), within a particular industry (an organ), that has metastasized now involving all nations and is affecting the entire earth (the host). Read more about this in Chapter 19.

Climate change: How do we know?

The International Governmental Panel on Climate Change published it’s 1435 page Report titled: Climate Change 2014, Mitigation of Climate Change. It was the Working Group III contribution to this fifth assessment Report. This Report is based on science, the study of the real world based on fact and truth, 1300 scientific experts performing and reviewing 1000s of studies and reams of scientific data. Here’s the conclusion of this Report:

‘Mitigation’, in the context of climate change, is a human intervention to reduce the sources or enhance the sinks of greenhouse gases (GHGs). Mitigation is necessary because Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC) have concluded that the consequences of unchecked climate change for humans and natural ecosystems are already apparent and increasing, and the dangers of irreversible damage are significant. While there are uncertainties, many scenarios lead to substantial climate impacts, including direct harms to human and ecological well‐being that exceed the ability of those systems to adapt fully. The planet as we know it is threatened. The energy supply sector is the largest contributor to global greenhouse gas emissions and therefore offers a multitude of options to reduce GHG emissions. But the stabilization of greenhouse gas concentrations at low levels requires a fundamental transformation of the energy supply system, including the long‐term phase‐out of unabated fossil fuel conversion technologies and their substitution by low‐GHG alternatives. As Renewable Energy penetrations increase, such issues are more challenging and must be carefully considered in energy supply planning and operations to ensure reliable energy supply, and may result in higher costs.

The International Panel on Climate Change issued a Special Report on Global Warming of 1.5 Degrees Celsius in October of 2018, summary below:

Limiting global warming to 1.5°C would require rapid, far-reaching and unprecedented changes in all aspects of society, the IPCC said in a new 2018 assessment. With clear benefits to people and natural ecosystems, limiting global warming to 1.5°C compared to 2°C could go hand in hand with ensuring a more sustainable world.

"One of the key messages that comes out very strongly from this report is that we are already seeing the consequences of 1°C of global warming through more extreme weather, rising sea levels and diminishing Arctic sea ice, among other changes," said Panmao Zhai, Co-Chair of IPCC Working Group I.

The decisions we make today are critical in ensuring a safe and sustainable world for everyone, both now and in the future, said Debra Roberts, Co-Chair of IPCC Working Group II. “The next few years are probably the most important in our history,” she said. “It’s a line in the sand and what it says to our species is that this is the moment and we must act now,” Roberts continued, “This is the largest clarion bell from the science community and I hope it mobilizes people and dents the mood of complacency.”

Christiana Figueres, the former UN climate chief who led the historic Paris agreement of 2015, said: “There is nothing opaque about this new data. The illustrations of mounting impacts, the fast-approaching and irreversible tipping points are visceral versions of a future that no policy-maker could wish to usher in or be responsible for.”

The report finds that limiting global warming to 1.5°C would require “rapid and far-reaching” transitions in land, energy, industry, buildings, transport, and cities. Global net human-caused emissions of carbon dioxide (CO2) would need to fall by about 45 percent from 2010 levels by 2030, reaching ‘net zero’ around 2050. This means that any remaining emissions would need to be balanced by removing CO2 from the air.  “Limiting warming to 1.5ºC is possible within the laws of chemistry and physics but doing so would require unprecedented changes,” said Jim Skea, Co-Chair of IPCC Working Group III.


Here is NASA’s perspective on Climate Change. All information below is from Global Climate Change – Vital Signs of the Planet at, except the text in italic. Note that on the diagram below CO2 levels are now over 400 parts per million, up from a peaks of about 300 ppm over the last million years.


The temperature of oceans has increased

Chapter 18

Climate Change