, 41 tweets, 15 min read Read on Twitter
To save human civilization, we need to panic and act NOW!

(A thread with simple explanations on why climate change is happening and its impact on our survival as a species)

1/ Important concepts to understand (that I'll expand in the thread):

- Where does CO2 in atmosphere come from
- Why CO2 in atmosphere makes the climate warmer
- Under which conditions did humans evolve in last 100k years
- What future conditions does warmer climate create

- What feedback loops accelerate warming
- How do scientists predict future warming
- How to interpret the probabilities of catastrophic events
- What's needed to prevent a collapse

It's going to be a LOOONG thread.

Fasten your seat belts, hold your seats. Let's go!
3/ The first thing to know is that earth has a natural cycle of warming and cooling (called glacial-interglacial cycle)

Due to natural variations in Earth's orbit, the ice cover in artic regions increases and decreases with a periodicity of 100k years ncdc.noaa.gov/abrupt-climate…
4/ Without human activity, Earth should actually have been cooling as the peak of last interglacial cycle, was tens of thousands of years ago.

The pre-industrialized, little ice age that happened during 1300 and-1850s is an example of what we should have been expecting.
5/ My tour guide in Paris said that during the little ice-age, people skated across the Seine river which was completely frozen.

Human activity has pushed the expected global cooling into global warming. The Little Ice Age ended with industrialization. en.wikipedia.org/wiki/Little_Ic…
6/ It is UNDISPUTABLE that the earth is getting warmer on average. See: berkeleyearth.org/2018-temperatu…
7/ What's the primary cause of this warming?

Primarily CO2 that gets produced when we burn our carbon-based fossil fuels. The carbon in those fuels combines with oxygen of atmosphere to produce CO2.

(Methane (CH4) also has the "greenhouse" warming effect.)
8/ CO2 warms the earth by trapping reflected solar radiation inside the atmosphere just like a glass window warms the car.

image via ohioenvironmentallawblog.com/2008/10/climat…
9/ CO2 levels in the atmosphere is the highest they have ever been. They stand at 400 ppm (particles per million), while historically they've stated around 200-250 range.

I REPEAT: in the history of human species, we have never seen such high CO2 levels. co2.earth/co2-ice-core-d…
10/ Did you notice the spike of CO2 level in the last 100 years? Yes, that's definitely us!

One evidence of human-created global warming is that our upper atmosphere is actually cooling as more radiation is trapped near lower atmosphere.
11/ One UNDERAPPRECIATED fact about CO2 is that it is a "stock" gas, not a "flow" gas.

This means the RATE of INCREASE in global temperature is related to its total quantity we've added so far and not just our current emissions rate.
12/ CO2 disperses slowly, remains in the atmosphere for centuries. This means that EVEN IF WE STOP OUR EMISSIONS today, global warming will continue

Note that even at zero emissions, our planet will be 1.5 deg warmer than pre-industrial levels. climateactiontracker.org/global/tempera…
13/ FYI: We're already 1 degree warmer than pre-industrial levels. weforum.org/agenda/2016/05…
14/ This one degree warming doesn't FEEL much when our daily temperature fluctuates so much anyway.

That's what I thought until I realized that this was GLOBAL AVERAGE, not a local maxima.
15/ Global means that locally, the variations are more. The artics are seeing a mean temperature increase of 2x higher compared to other regions.

16/ Average means that EXTREMES are going to be much hotter.

17/ The effect of increased carbon dioxide on human life is hard to estimate but know that FIVE out of the last SIX mass extinctions of life on earth happened because of warming due to greenhouse gases.

18/ Actually, we don't have to wait until human extinction. The effects are already there and will be seen.

- The storms are more frequent and more intense
- Unprecedented heat and cold waves
- Drought and wildfires
- Human migration related to climate impact
19/ As sea levels rise and coral reefs die, our coastal population WILL immigrate and 2 out of 3 world's megacities are based on or near coasts. If Mumbai, New York and Bangladesh flood, it'll impact the entire world.
20/ We're NOT prepared for this.

(Not to mention that the tropical regions will have heat so extreme that humans will migrate from there as well)
21/ The United Nations hosted IPCC predicts massive impacts to HUNDREDS of MILLIONS of people if our climate warms from 1 degree to 2 degrees.

Please read this summary of the report: ipcc.ch/sr15/chapter/s…
22/ IMMINENT actions they recommend to countries:

Recommendation #1: Cut emissions by 45% by 2030 (in 10 years) and to zero by 2050

This seems unlikely because emissions are INCREASING every year nature.com/articles/d4158…
23/ Recommendation #2: remove carbon dioxide from atmosphere.

Only cutting emissions will not do. CO2 is a stock gas and disperses slowly. We will have to start removing it. Sadly, the tech is unproven to scale :(

Even planting more trees may not help: nature.com/articles/d4158…
24/ By the way, we have confidence in climate change prediction models because we run them for past conditions and see that they match the observed data.

25/ So we better take IPCC's future projections seriously.

In the high emissions scenario (the path that we're on), global average surface temperature could be as high as 8 degrees beyond conditions humans have ever faced.

26/ IPCC provides ranges for future projections. We latch on to median projections. (Say the Paris 2015 UN agreement between countries of keeping the temperature below 1.5 degrees)

We can't process percentiles or ranges.

What does a 10% chance of human extinction mean to you?
27/ Unfortunately, IPCC has a history of under-estimating. Usually, their worst-case scenarios, and not medians, come true because:

- They don't employ natural feedback loops that accelerate warming
- They are polite because of politicial negotiations

28/ Feedback loops in nature are what worries me because they are hard to model.

One example of the albedo effect.

More warming -> less ice cover -> less white snow -> less solar radition reflction -> more absorption by darker water -> more warming
29/ These positive feedback effects mean that we could push Earth's climate system into a fundamentally different trajectory for centuries.

30/ This 'hothouse' earth trajectory could mean that instead of seeing arctic ice-free in summers in the next 10 years, we could see that as soon as next year (or so).

Warming is not linearly increasing, it is accelerating due to feedback loops.
31/ Last five years were the warmest on record, and March 2019 was the second warmest since records were started to kept (after 2016).
32/ Unfortunately, it may be too late.

There's a paper that's sending people to depression clinics. It asks us to abandon the hope of our values of the past, the expectation of unbridled economic growth and rethink our relationship with earth.

33/ What baffles me is that in spite of all the evidence, there are people who still deny climate change.

A leader's rejection of climate change may be the biggest crime they can commit. @realDonaldTrump, I'm talking about you.
34/ Know that media over-represents climate change deniers.

There's 97% scientific consensus and yet media shows that there are two sides to the global warming debate. iopscience.iop.org/article/10.108…

Journalists, YOU CAN DO BETTER!
35/ If not already, climate change will become an existential threat for human civilization. The mad max scenario is a possibility, if not outright wipeout.

What *could* be more important than preventing the human civilization from falling apart?
36/ Remember: we can argue with humans but we can't argue with climate.

The human body has evolved to work in a very narrow band of temperature, our culture has evolved around historically stable climates. With climate changing, everything we know or care about will change.
37/ What can you do? Because of urgency of the situation, the only thing I can think of is political action.

Climate should be NUMBER 1 policy point for any politician. We should protest or vote for urgent government action. #ExtinctionRebelion is a great example.
38/ Time to sit back and observe is up. We need to panic.

Even if we're wrong and don't hit the doomsday predictions, we'd end up having a more thoughtful relationship with the earth. Everything we depend on comes from there ultimately. Yes, even our iPhones!
39/ That's all folks.

It was a long thread, but hopefully, it'll help you become more aware of what's happening around us.

Please consider retweeting the thread so more people understand climate change.
40/ Found this fantastic talk on the mathematics of climate change:

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