Convergence: The Basis of 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 the findings of independent research move towards the same overall conclusion, they support one another, fitting together like jigsaw puzzle pieces. 

Scientific confidence grows as convergence grows stronger.  This happens when:

  • More investigations support the same conclusion,
  • The range of methods used grows, and
  • Research rules out opposing conclusions.

For example, you can be more confident of the distance between two buildings after you measure it in more ways and get close results, say 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 finding can contradict and over-turn a widely accepted conclusion.  However, when there is a strong convergence of evidence supporting the accepted conclusion, it is likely that the contradiction is ill-founded.

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. 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, based on the axioms that define that mathematical system. So, mathematicians can provide proof: 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 stronger convergence supporting a conclusion, you can have more confidence in that conclusion.

Convergence and climate change

Scientists are very certain 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 of 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.

For a start, considering many lines of independent and diverse research, the evidence 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. This is what the evidence shows:

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

We know that carbon dioxide scatters heat radiation, decreasing the escape of heat 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 the 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, the study to reach each of the above findings is itself 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 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 certain that we are experiencing human-caused climate change.

This time, popularity suggests convergence

Ninety-seven percent of climate scientists agree that humans have caused the current global warming. And most of the leading scientific organizations 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, and scientific certainty is not determined by popularity. What is the relevance of this popularity?

As nearly all climate scientists support the consensus view, we can assume that the line of research taken by each of these scientists supports the consensus view. This means that many independent lines of research converge on the consensus view. It also means that 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, the “general theory of relativity” predicted that massive objects bend light. Scientists then confirmed this by observing stars close to the sun during an eclipse. They saw that the sun did bend the starlight as it passed close to the sun. This confirmation increased confidence in the theory.

Understanding the nature of carbon dioxide provides an explanation of the current global warming and 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 a warming of from 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

While there are many aspects of climate change that still need to be explored, scientists have understood the nature of carbon dioxide for a long time. With increasing accuracy, they have predicted that increasing levels of carbon dioxide in the atmosphere would increase temperatures. Science provides an explanation of global warming. Predictions based on this understanding have been confirmed, and continue to be confirmed as the globe warms and the climate changes.

The key message.

Scientists have great confidence in the concept of “human-caused climate change”. They base this 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 inordinate amounts of effort into trying to find something that is wrong with climate science. And climate scientists, in their search for what is really happening, have also worked hard at finding something wrong with the conclusions of climate science. 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)

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 12 March 2019

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