When we think of science, we often think of
the *scientific method*. But calling it *the*
scientific method is a bit misleading. There’s
no single scientific method. There are a number of
ways that scientists can improve their understanding
of how the natural world works. And it doesn’t
happen in a single step. The process of building
scientific understanding happens over time.
Let’s explore the different processes that
contribute to our scientific understanding.
One approach is called the deductive method.
This involves first coming up with a hypothesis,
a possible explanation of how the world works.developing a better understanding of the mechanisms of the natural world
In science, a hypothesis is no good unless
it can generate predictions. Then scientists
collect observations to see whether that prediction
comes true.
For example, in 1859, John Tyndall made some
predictions about what warming from increasing
greenhouse gases should look like. He predicted
that if greenhouse gases were causing warming,
then we should see nights warming faster than
days, and winters warming faster than summers.
Around 150 years after that prediction, scientists
finally had the opportunity to test Tyndall’s
prediction. It turns out his prediction was
right. The data confirmed his prediction,
and is one piece of evidence for greenhouse
gas warming.
Let’s look at a counter example, where the
data disproves a hypothesis. In the early
20th Century, some scientists thought that
the oceans were big enough to soak up all
the extra carbon dioxide we were emitting
from fossil fuel burning. In the 1950s, Charles
Keeling began taking detailed, comprehensive
measurements of atmospheric carbon dioxide.
Year after year, he took the most accurate,
comprehensive measurements of CO2 that had
ever been taken. Within a few years, it became
clear that atmospheric carbon dioxide was
increasing. The oceans weren’t absorbing
*all* of our CO2 emissions - some of it was
staying in the atmosphere. The data showed
that the notion that the oceans would take
up all our CO2 emissions was incorrect.
Another scientific approach is called the
inductive method. This involves collecting
the data first, then scientists analyse that data to see if they can detect any patterns. Once a scientist has 
analysed the data and developed a hypotheses, whether it be using the inductive or deductive method,
 the job isn’t done yet.
Before research can get published in
a scientific journal, it gets scrutinised
by other scientific experts. This process
is known as peer-review. What it strives to
do is weed out errors, making sure the research
is rigorous and evidence-based. Peer-review
is not a guarantee that the scientific research
is perfect, mistakes still get publsihed in scientific journals. But because of the level of scrutiny,
I would argue that peer-reviewed research
is the highest quality source of scientific
information available.
Okay, so a scientist has collected data, analysed
it, developed a hypothesis, survived peer-review
and got their research published in a scientific
journal. The job is done, right? Not
even close. When scientific research has been
published, the next step is other scientists
check the results by trying to replicate it.
They run their own experiments or take their
own measurements to see if they obtain the
same result. When a result is replicated independently,
we have more confidence that it’s accurate.
When a result is replicated by completely
different types of measurements, then our
confidence is even stronger.
For example, there are a number of different
ways to check whether humans are causing global
warming. Observing nights warming faster than
days, or winters warming faster than summers, are just
two human fingerprints. Our climate is rich and complicated and we expect
to see a whole range of different human fingerprints.
For example, we should see the upper atmosphere cool at the same time that the lower atmosphere warms. It's a completely independent observation to changes
in the daily or yearly cycle, but the conclusion
is the same: humans are causing global warming.
When independent lines of evidence all point
to the same consistent conclusion, scientists call this
a consilience of evidence. As the body of
evidence builds up, what follows is overwhelming
agreement among the scientists - a scientific
consensus. In and of itself, consensus doesn’t
prove that a hypothesis is correct. Our confidence
in a scientific proposition comes from the
evidence. Scientific consensus is a reflection
of our scientific understanding.
The common thread running through all of this
is a reliance on scientific evidence. Whether
the scientific method is inductive or deductive,
evidence is a crucial part of the process.
Our confidence in the result strengthens as
more lines of evidence build up. It should
be only when a consilience of evidence has
developed that a scientific consensus forms.
