How Sure Are Climate Scientists, Really?

when experts warn us about something like they do with climate change they're never 100 sure so how do we know when they're sure enough they tell us that a few degrees can make a world of difference twenty thousand years ago the earth was about to come out of an ice age glacial ice sometimes two miles thick covered much of the northern hemisphere [Music] and the ice consumes so much water that the sea level was over 100 meters lower than today solo that asia and the americas were connected by a land bridge and many of today's

islands weren't islands at all scientists might also explain that some of the details may be a bit fuzzy but they're still confident that by and large this is what our earth was like as the filmmaker i don't entirely know how they know these things or what makes them so sure but that's okay isn't it to just report what the experts say well well the doctor is in on a new study suggesting coffee could be the latest cnn reports in some fields of science like nutrition the warnings we've received from experts have been unclear meat may

not be as bad by now we've been told so many conflicting things about which foods will make us live longer get sick or lose weight that trust has with eroded and minerals not anymore now we want people to eat the whole food now some say journalists are to blame for reporting new health studies without enough explanation about the underlying science but scientists themselves have apparently been making mistakes determining how reliable their results are and it's not just newscasters and nutritionists who struggle with uncertainty we're learning that a significant number of experiments in psychology and some

areas of medicine can't be replicated or verified because the researchers in many cases overstated the strength of their findings now on one hand climate science has a basis in so-called hard sciences like geology and physics which are less prone to replication problems than research about human behavior sometimes called soft science or social science on the other hand climate change is about humans right so do we need both hard and soft sciences to understand it let's explore this with some carbon arithmetic say we wanted to know how much carbon dioxide has been added to the atmosphere

by humans well we know how much fossil fuel has so far been burned and we know how much co2 would be produced as a result and we know deforestation releases additional co2 but not all this extra carbon stayed in the atmosphere because most of it got absorbed by the oceans and soils now there is some uncertainty surrounding these numbers but ultimately we can check our math against air water and soil samples grounding our final answer in hard science evidence but we see the science get softer when we ask a different question how much fossil fuel

is left to economically mine and burn the arctic may hold a quarter of the earth's undiscovered oil answering this requires making predictions about future discoveries energy markets and whether countries enact policies that somehow keep fossil fuels in the ground california stands to gain if more fracking is allowed categorizing the sciences like with hard or soft can be useful if it helps us identify what research is more trustworthy but people studying the replication crisis are still figuring out how widespread it is and what can be done about it it's a big active topic of debate but

i'm interested in how journalists and people like me are supposed to report on science given all these open questions so here i'll share why i've come to believe that even when looking at climate research the only way to learn how sure scientists are is to dig in a little and view their work with some healthy skepticism so here we're looking at the earth's temperature 20 000 years ago the negative numbers indicate how many degrees colder it was in celsius than the late 1900s the temperatures are estimated by looking at ice drilled out of glaciers as

well as fossils such as shells that hold clues about the conditions when they are formed and this particular data comes from a study that combines 80 temperature records from different locations it's the most comprehensive study i could find for this time period published in a major journal the researchers averaged all these messy lines together weighing them differently based on location and other factors and they express their confidence level using a margin of error in this case with 68 percent confidence but here's a case where the margin of error doesn't seem to mean that much because

none of the climatologists i spoke to including the authors of this very study were 68 sure that the true temperature lies between these dashed lines they all said it's probably lower because another study that just focused on the last ice age put the average temperature here this ice age study is considered to be more reliable because it factored in more types of evidence and did more robust modeling margins of air can be skewed for all sorts of reasons which is why talking to scientists can help reveal how sure they really are in this case the

climatologists were okay with me using the shape of this timeline as long as it was shifted downwards to agree with the more reliable ice age temperature and they were not comfortable with me showing numbers pulled straight from the single study and i wasn't comfortable at first questioning numbers published by credible experts but that's just it to improve how health and nutrition get reported journalists need to scrutinize even filter what gets publicized beyond is ensuring studies are peer-reviewed and published in a major journal which means people who aren't called scientists kind of have to be scientists

now error margins can be misleading for other reasons too certainty is often too complicated to be summed up as a simple number or phrase for example this graph may be too smooth which is relevant to the climate debate short-term variations like this or this could have occurred but the level of precision in the underlying data kind of blurs the image variations this big however are unlikely to have happened without leaving a mark in the natural record but a smooth over line does show long-term trends and you may have noticed the temperature has been creeping upwards

do scientists understand why while the earth's orbit is composed of many different cycles of different duration we experience the daily and yearly cycles in a dramatic way but some more subtle repetitions occur over tens of thousands even hundreds of thousands of years and the accumulated effects of these long-term cycles tracks with evidence of ice ages which you can see in some places but in other places it doesn't line up that well well that's because scientists explain the relationship is complex the orbital changes didn't directly cause the temperature to rise because they didn't cause more sunlight

overall to hit the earth they did affect the angle of the sun in a way that allowed morbid to reach the poles which caused the glaciers to retract which meant the earth was less reflective so it absorbed more sun and there are new sea currents and carbon dioxide levels increased though scientists aren't exactly sure why and all these secondary factors cause the average temperature to rise scientists say they have a pretty good understanding of this but even when the world seems to be in clear view the picture is always at least a little bit out

of focus obscured distorted another reason scientists can't reliably tell us how sure they are is that often they don't know how close they are to the truth and they're prone to confirmation bias and often under pressure to publish noteworthy findings even the guiding principles of science itself aren't set in stone key concepts have been rebuked and revised until the mid-1900s scientists believe that discoveries are made by observing their surroundings and making logical conclusions a process called empiricism then they realized that acquiring knowledge was a more imaginative process to cut through the fog scientists have to

make guesses on top of what they know and then test these guesses so imagination when paired with scrutiny is central to the discovery process and uncertainty the very thing that clouds our view also frees us to construct possible answers climatologists have built models that help them predict how different forces affect each other and impact the earth's temperature like the way meteorologists use models to forecast the weather they grow more certain when experiments confirm their theories when different types of evidence agree and when theories survive critical review from others plus these models have been around long

enough now that we can look back and see how well they predicted changes that have already occurred now let's shift gears and look at what humans were doing since that last ice age shrinking ice sheets allowed humans to cross that land bridge we saw earlier between asia and north america sometimes melting glaciers would collapse causing massive floods or abrupt sea rise farming would ultimately lead to the birth of civilization which spread slowly across the globe [Music] cities would grow larger governments more powerful empires would rise and fall [Music] so much history happened through these centuries

as territories were settled conquered reconquered big discoveries would change the world [Music] but from a core numbers perspective the really big changes were about to happen somewhere around here something dramatic happened the age of enlightenment and the industrial revolution now some say the enlightenment began around here but never ended it marked the moment we rebelled against so-called authorities of truth primarily religious institutions and monarchs and the result was a period of unprecedented discovery scientists will say they're different from authorities of truth because they don't want others to take them at their word they encourage fellow

scientists to challenge and test their explanations as for non-experts we've discussed how problems can emerge when journalists treat experts like authorities of truth and there's a growing concern that for the public trusting or distrusting scientists is becoming a matter of political identity caveats aside the scientific revolution corresponded with an enormous uptick in human well-being advances in medicine agriculture and sanitation allowed us to live longer and healthier lives our population exploded some might say we thrived but population growth combined with the industrial revolution had environmental consequences the amount of carbon dioxide in the atmosphere began rising

due primarily to the burning of fossil fuels the first reliable thermometer was invented in 1714 which allows to collect good temperature data from around the world and this dark line is nasa's construction of the global average one could argue that scientists were slow to grow certain of human-caused climate change some studies warned of the problem well over a hundred years ago in 1965 the u.s president's science advisory committee issued a major report stating that carbon dioxide quote will almost certainly cause significant changes in the temperature since then the earth's temperature has been rising [Music] looking

back at the 20 000 years we just traveled the recent warming looks different than past natural changes now i've made a point to highlight uncertainty that clouds this chart other skeptics have raised other questions some credible some not but you're not a reasonable skeptic unless you're willing to size up your doubts with the larger picture of truth uncertainty may not translate into simple numbers but we can still gauge as best we can whether there's enough of it to change the picture even compared to moments when we were exiting the ice age the most rapidly today's

rate of warming is of a different magnitude and it started abruptly when according to the cycles temperatures should be flat or waning and still scientists were able to predict it and they explained it with evidence and reason now to estimate future temperatures climatologists must rely on their models and make a number of assumptions one being human behavior this scenario by the international panel for climate change assumes we make no new efforts to reduce carbon emissions whereas this one assumes we make drastic cuts enough to keep temperature rise to two degrees above pre-industrial levels and the

gap between these scenarios highlights uncertainty stemming from the fact that we don't know what humans are going to do the realm of soft sciences but what about uncertainty stemming from the hard science well the ipcc projections do specify a margin of error which here they get by comparing the temperatures submitted by the teams of scientists behind the ipcc who've each crunched their own numbers and if this chart looks messy to you it is depending on how the teams designed and configured their models they got different results but you can see consistency too all the teams

found that greater carbon emissions will result in significantly higher average temperatures so even if models can't simulate reality perfectly they can do it well enough to help us learn and solve problems and here they're helping us figure out what we need to do to bring our planet's runaway temperature under control now some have argued that because uncertainty exists in the hard science we should hold back our efforts to change our behavior in fact here are examples when prominent figures in the u.s have pointed to uncertainty as a reason to defer policy now if you pause

and read about these cases you might find that many look more like political maneuvers than honest arguments about the science still uncertainty is a prevailing theme of the climate debate and refuting these arguments with reason takes some work especially because uncertainty is confusing even for the experts a simpler rebuttal is to say we just need to trust the scientists we can point out that they know the subject matter that there's a consensus within the field and a peer review process and that credible institutions back their claims now notice these arguments are all about endorsing the

experts not about the merits of what the experts are saying or the science there are lots of good reasons to trust experts i mean we have to our society functions thanks to specialized occupations but when somebody questions whether a finding is true saying trust the scientists is a problematic answer because we know individual scientists are fallible and that individual studies have made false claims and more importantly that systemic problems have led influential groups of scientists to make mistakes and we know that the scientific revolution was built on the idea that we don't take people at

their word because we reject authorities of truth which is why it's so important for non-experts to on occasion wade into the science now with the aim of understanding an issue completely that's impossible but enough to understand why say these claims are unreasonable and a beautiful thing happens when we point out that scientists and their ideas are fallible we're reminded that we can get better at science and better at explaining science and better at determining as a society when scientific claims can be believed with confidence enough confidence to take action as is clearly the case with

the climate mind you people with and without phds are prone to overconfidence when predicting human behavior and this false sense of knowing people can take many forms i personally struggle with climate defeatism a feeling that this line has already been drawn since realistically humans won't change quickly enough to dramatically bend its shape and without a drastic bend efforts to fight climate change will only delay the inevitable [Music] the fetus might take comfort and inevitability the way denialists take comfort and uncertainty [Music] it takes the pressure off we defeat us may call ourselves realists but really

we're just overly certain and perhaps unimaginative scientists a century ago the empiricists were wrong about how discoveries were made because they didn't appreciate how important imagination is how it allows us to reach out beyond what we can see and compose answers even about things that were true all along laws of nature so surely imagination grounded in hard science knowledge can be of use when forecasting a future of our own making [Music] but to devise and then rally behind a good plan we first have to believe and i mean really believe that our future is uncertain

[Music] because only then might we be so bold as to shape [Music] i'm going to follow up this video by looking at ideas for tackling climate change and when i say look at i mean skeptically scrutinizing the numbers please follow me on social media and consider supporting my work on patreon [Music] [Music] you