Scientific confidence on climate change is based on an enormous convergence of evidence.
The basic conclusions are that:
- Global warming is occurring, and
- It is very likely that humans are the cause.
The Convergence of independent lines of inquiry
Scientists have great confidence in this consensus position because many lines of independent scientific research converge on and so support the consensus position.
In science, and indeed in every day life, the greater the number of independent bits of data that fit together, like the bits of a jigsaw puzzle, and present a cohesive conclusion, the greater the confidence in the conclusion.
A common example of this is when people are working out how much to bid on a house at an auction. You could consider:
. an estimate from the selling estate agent,
. estimates from other estate agents, and
. the prices of a similar homes sold recently.
The more that independent bits of information fit together, the greater can be your confidence in your estimate.
Dr Willis, the Director of the “Royal Institution of Australia”, discussed “consilience” [convergence] on ABC radio: The Science Show. He said:
The vast majority of climate scientists are in one camp. However, this, by itself, is not particularly helpful. Science is not a democracy.
[Scientific confidence] is all about the evidence. … Let me introduce a concept that is all too often overlooked, that can actually explain the anatomy of a scientific debate.
Consilience [or convergence occurs when] several different lines of inquiry converge on the same or similar conclusions. The more independent investigations you have that reach the same result, the more confidence you can have that the conclusion is correct.
What has [had little publicity is that the convergence] of evidence for anthropogenic climate change is particularly strong.
The IPCC reports [see below] are a consilience of hundreds of independent lines of evidence all converging on the same or similar conclusions. … This is then magnified because of the convergence of (1) the investigations within climate change research, and (2) the findings of the rest of science. They all point to the same conclusions about how the world works, with climate change comfortably nested within all the other scientific disciplines.
An example of multiple lines of inquiry within climate science
As an example, scientists working on the “average global temperatures” over the last 800,000 years are informed by multiple lines of inquiry including: (1) thermometer readings, (2) satellite records, (3) balloon records, (4) tree ring data, (5) ice core data, (6) coral reef data, and (7) fossil data.
(Temperature Record: Wikipedia)
These multiple lines of inquiry offer independent evidence of global temperature. The more independent investigations you have that reach the same result, the more confidence you can have that the conclusion is correct.
Confidence about climate change conclusions
Naomi Oreskes writes that the convergence of many lines of research is what provides very strong support for the scientific consensus on climate change. (Oreskes, 2007, p 26 of 36)
Anthropogenic global climate change is no longer a subject of scientific debate. (Oreskes, p 9 of 36)
Nearly all climate scientists agree
The Scientific Consensus (NASA) states that ninety-seven percent of climate scientists agree that:
- Global warming is occurring, and
- It is very likely that humans are the cause.
This is strong support for the scientific consensus position, as it indicates the convergence of the lines of research of these ninety-seven percent climate scientists.
These two propositions are no longer a subject of scientific debate.
(The Scientific Consensus on Climate Change: How do we know we are not wrong?, Oreskes, p 9 of 36)
It’s NOT true that many leading scientists question climate change
(Climate myths: Many leading scientists question climate change: New Scientist)
There are contrarians in most sciences
Now, 3% of climatologists do not endorse the scientific consensus position.
“In a way, such climate-change scepticism is unsurprising. A denialist [contrarian] fringe operates at the margins of almost any important field of science that gets discussed widely in the public domain. The most egregious example in my [medical] field is the faction that [still] claims the human immunodeficiency virus (HIV) does not cause AIDS.” (Sceptical Thinking: Peter Doherty)
No one has faulted the basic IPCC conclusions
Contrarians have put inordinate amounts of effort into trying to find something that is wrong with climate science. In their search for what is really happening, climate scientists have also worked at finding something wrong with the conclusions of climate science. And despite all this effort, everyone has come up empty-handed. (Oreskes, p 25 of 36)
Evidence for global warming has only grown
Year after year, the evidence that global warming is real and serious, has only strengthened. (Oreskes, p 25 of 36)
Most scientific organizations endorse the consensus position
“Most of the leading scientific organizations worldwide have issued public statements endorsing this [consensus] position.”
(The Scientific Consensus: NASA)
Some of these organisation are:
** American Association for the Advancement of Science: See the AAAS Scientific Consensus on Climate Change
Again, this the support for the consensus position gives confidence as it indicates the convergence of many lines of research of the members of these scientific organisations.
The physical sciences do not offer “proof”
People who demand “proof” about climate change are demanding the impossible.
There is no proof that the current climate change has been caused by humans burning fossil fuels and forests, releasing carbon dioxide. That is because the physical sciences cannot offer proof, they offer hypotheses of varying degrees of confidence.
It is mathematics that offers proof, proof of mathematical statements based on well defined assumptions.
The relevant question is how confident are scientists that the current climate change has been caused by humans burning fossil fuels and forests, releasing carbon dioxide.
As described on this page, the scientific community has extremely high confidence in the basic conclusions about the current climate change – due to the convergence of many independent lines of research.
The International Panel on Climate Change (IPCC)
In more detail, the findings of climate science are in the reports from the “International Panel on Climate Change” (IPCC). An IPCC report in 2013 stated:
“Warming of the climate system is unequivocal [very clear], and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased
Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years.
The oceans have warmed, accumulating more than 90% of the energy accumulated by our planet between 1971 and 2010.
Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent.
The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification.
The largest contribution to [global warming] is the increase in the atmospheric concentration of CO2 since 1750
It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”
The IPCC is a World Authority on Climate Science
The International Panel on Climate Change (IPCC) is an internationally accepted authority on climate change, producing reports by leading climate scientists as agreed with participating governments.
Thousands of scientists and other experts contribute, on a voluntary basis without payment from the IPCC, to writing and reviewing reports, which are then reviewed by governments. The IPCC reports contain a “Summary for Policymakers” which is subject to line-by-line approval by delegates from all participating governments. Typically this involves the governments of more than 120 countries.
(International Panel on Climate Change, Wikipedia)
Confidence about these conclusions
Scientists have confidence in the consensus position because many lines of independent scientific research converge on the consensus position.