Convergence brings scientific confidence

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

Scientists are supremely confident that we are experiencing human-caused climate change. This is because there is an overwhelming “convergence” of evidence supporting this conclusion. So, what is convergence?

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 when:

  • more investigations support the same conclusion,
  • the number of investigative methods increases, and
  • research rules out alternative hypotheses.

For example, you can be more confident about the walking distance between two buildings when:

  • a measuring tape indicates 30 meters,
  • a laser range finder indicates 29.1 meters, and
  • a ground-penetrating radar rules out a rumoured shortcut tunnel.

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 literally the “jumping together” of knowledge

Science offers convergence, not proof.

People who demand proof about climate change are demanding the impossible – and these people 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).

Even within mathematical systems defined by a precise set of axioms, Godel’s Incompleteness Theorem shows that you cannot prove the truth of some true statements. If mathematics cannot always supply proofs, it’s ill-informed to demand proofs of science.

Science does not offer proof. Science offers conclusions that have varying degrees of confidence. When you have greater convergence supporting a conclusion, you have greater confidence in that conclusion.

Beware of people demanding proof that global heating is happening.

Convergence and climate change

Scientists are supremely confident that humans have caused the current climate change. This is because there is an overwhelming 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 heating. For example, the current global heating 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 heating at an increased rate over this period.

Independent and diverse research supports the conclusion that “global heating is occurring”.

It’s consistent with global heating that the following things are happening together. And the evidence shows that these things are happening together:

Sea level is another independent measure of global heating that also points to global heating. As the planet heats sea levels increase due to (1) water expanding as it heats, and (2) land ice melting and flowing into the oceans.

Carbon dioxide scatters heat radiation, decreasing the amount of heat that escapes from our planet into space. So, as carbon dioxide levels rise, temperatures tend to increase.

Humans are burning fossil fuels, producing vast quantities of carbon dioxide, so, unsurprisingly, carbon dioxide levels are increasing.

As CO2 in the atmosphere increases, more CO2 dissolves in the oceans, forms carbonic acid and increases ocean acidity.

The evidence for global heating does not come from one scientist with a thermometer measuring air temperature in one location. The evidence comes from many scientists measuring many things, i.e., conducting diverse and independent lines of research. And this evidence converges on one central conclusion. We are experiencing human-caused climate change.

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

We also have the reports produced by the International Panel on Climate Change (IPCC), which bring together the work of hundreds of scientists. 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 heating. 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 independent lines of research support the consensus view. This diverse research converges on the consensus view. The very wide range of science included within climate science means that the popularity of the consensus view demonstrates convergence and provides 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 confirmed.

For example, Newtonian theory predicts that light will bend when it passes close to the sun. However, Einstein’s General Theory of Relativity predicts that the sun would bend light twice as much – and scientists confirmed this larger bending by observing stars during an eclipse. This confirmation increased confidence in Einstein’s theory.

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

  • 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 the doubling of CO2 would give heating 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 heating between 1972 and 2000

Science explains global heating. While scientists still need to explore many aspects of climate change, they 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 measurements have 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 and 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 heating has only grown.

Year after year, the evidence that global heating 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 R dio: The Science Show: (click to see transcript)

The 97% consensus on global warming
Skeptical Science

History of climate science: Wikipedia

Updated 3 January 2024

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