Convergence brings scientific confidence

Image of convergence: A red arrow and five blue arrows meet point to point

Paths converge when they move towards the same point and come close or meet.

In science, convergence occurs when independent research findings move towards the same overall conclusion, supporting and fitting together like jigsaw puzzle pieces. 

Scientific confidence grows as convergence increases by:

  • more investigations supporting the same conclusion,
  • the number of investigative methods increasing, and
  • research ruling out alternative hypotheses.

For example, you can be more confident about the distance between two buildings when you get close results by measuring it using different methods, e.g., using a measuring tape and a laser range-finder. If people talked of a shortcut tunnel between the buildings, you could search using ground-penetrating radar. Given no evidence of a tunnel, you could rule that option out, and the evidence would converge on a firmer conclusion.

One new finding can contradict and overturn a widely accepted conclusion. However, when there is a strong convergence of evidence supporting the accepted conclusion, the new finding probably contains an error.

Convergence is also called “concordance” or “consilience”. Consilience is the “jumping together” of knowledge.

Science offers convergence, not proof

People who demand “proof” about climate change are demanding the impossible. They are often intent on generating confusion about climate change.

“Proof” is “evidence sufficient to establish a fact”, and “a fact” is “a thing certainly known” (Oxford dictionary).

You can prove that a mathematical hypothesis is true using the axioms that define that mathematical system. So, mathematicians can provide proof, i.e. the evidence to establish a thing as certainly known and with 100% certainty.

Science cannot do this. Science offers conclusions that have varying degrees of confidence. When you have greater convergence supporting a conclusion, you can have greater confidence in that conclusion.

Convergence and climate change

Scientists are very confident that we are experiencing “human-caused climate change” as there is a strong convergence of evidence supporting this conclusion:

  • Evidence from many lines of research supports this conclusion,
  • The research methods used are diverse, and
  • Research has ruled out many alternative explanations for global warming. For example, the current global warming is not due to an increase in the sun’s energy. The sun’s output has decreased since the 1980s, and the Earth has been warming at an increased rate over this period.

Independent and diverse research supports the conclusion that “global warming is occurring”. It is consistent with global warming that the following things happen together: (1) temperatures increase, (2) ice levels decrease, (3) ocean temperatures increase, and (4) coral bleaching increases. The evidence shows that:

Sea level is another independent measure of global warming. Water expands as it warms. So, as ocean temperatures increase, sea levels tend to rise. And, as land ice melts and the melt-water flows into the oceans, sea levels tend to increase.

Carbon dioxide scatters heat radiation, decreasing heat escape into space. So as carbon dioxide levels rise, temperatures tend to increase.

Humans are burning fossil fuels, producing vast quantities of carbon dioxide, so it is not surprising that carbon dioxide levels are increasing.

As CO2 in the atmosphere increases, it makes sense that more CO2 becomes dissolved in the oceans, forming carbonic acid and increasing ocean acidity.

Here we have evidence from many diverse and independent lines of research. And this evidence converges on one central conclusion. We are experiencing human-caused climate change.

Note that the study to reach each of the above findings is complex. For example, scientists working on the “average global air temperatures” over the last 800,000 years are informed by multiple independent 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

Then we have the reports produced by the International Panel on Climate Change (IPCC), which bring together hundreds of scientists’ work. The IPCC reports present the convergence of hundreds of independent lines of research.

This enormous convergence of diverse evidence is why scientists are very confident that we are experiencing human-caused climate change.

For climate change, popularity suggests convergence.

Ninety-seven percent of climate scientists agree that humans have caused the current global warming. And most of the leading scientific organisations worldwide have issued public statements endorsing this consensus view.
The Scientific Consensus (NASA)

So nearly all climate scientists accept the consensus view. However, science is not a democracy where popularity determines direction. What is the relevance of this popularity of the consensus view on climate?

As nearly all climate scientists support the consensus view and climate science incorporates many fields, we know that many lines of research support the consensus view. This diversity of supportive research gives convergence on the consensus view. In this situation, because of the wide range of science included within climate science, the popularity does provide confidence in the consensus view.

Here is an article about the climate consensus and the misrepresentation of climate science.
Mining director Ian Plimer misrepresents climate consensus studies in the Australian Newspaper.
(Desmogblog: 25 Jan 2019)

Scientific certainty and prediction

Confidence in a theory increases when the theory explains a phenomenon, particularly when the theory leads to a prediction that is then confirmed.

For example, Newtonian theory predicts that light will bend when it passes close to the sun. Then, Einstein’s “general theory of relativity” predicted that the sun would bend light twice as much – and scientists confirmed this by observing stars during an eclipse. This confirmation increased confidence in Einstein’s theory.

The nature of carbon dioxide explains the current global warming, and this understanding led scientists to predict global warming.

  • In the 1890s, a Swedish scientist, Svante Arrhenius, calculated that cutting atmospheric CO2 in half would be sufficient to produce an ice age. And that doubling of CO2 would give warming of 5 to 6 degrees Celsius. He also realised that human emissions of CO2 could increase CO2 in the atmosphere and warm the planet.
  • In 1972, John Sawyer accurately predicted the rate of global warming between 1972 and 2000

Science explains global warming. While many aspects of climate change still need to be explored, scientists have understood the nature of carbon dioxide for a long time. With increasing accuracy, they have predicted that rising atmospheric carbon dioxide levels would increase temperatures. Scientists have made predictions based on this understanding, and subsequent measurement has confirmed these predictions.

Confidence in human-caused climate change

Scientists have high confidence in the concept of “human-caused climate change”. They base this confidence on the convergence of evidence from very many independent lines of research.

No one has faulted the basic IPCC conclusions.

Some people work hard to sow doubt about climate science. They have put enormous effort into finding something wrong with climate science. In their search for what is happening, climate scientists have also worked hard to find something wrong with climate science’s conclusions. 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 severe has only strengthened. (Oreskes, p 25 of 36)

Sources on Convergence

The Scientific Consensus on Climate Change: How do we know we are not wrong: Naomi Oreskes: 2007

Consilience powers the big scientific ideas
Dr Willis: Director: Royal Institute Australia
ABC Radio: The Science Show: (click to see transcript)

The 97% consensus on global warming
Skeptical Science

History of climate science: Wikipedia

Updated 5 April 2021

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