Climate Change Is, In General, Not An Existential Risk

Link post

[Every­thing in this post is true to the best of my knowl­edge, but I am not a cli­ma­tol­o­gist and my last sci­ence class was in high school. It is very likely I have mi­s­un­der­stood some­thing. I wel­come cor­rec­tions. Ded­i­cated to An­nie.]

I of­ten see peo­ple say that cli­mate change is go­ing to kill us all, or that hu­man ex­tinc­tion is in­evitable due to cli­mate change, or that if effec­tive al­tru­ists were re­ally con­cerned about ex­is­ten­tial risk we would put lots of effort into fight­ing cli­mate change be­cause all sci­en­tists agree that is the biggest ex­is­ten­tial risk.

As far as I can tell, ab­solutely none of this is true.

Cli­mate Feed­back, a non­par­ti­san web­site ed­u­cat­ing peo­ple about the sci­en­tific con­sen­sus on cli­mate change, has writ­ten about hu­man ex­tinc­tion from cli­mate change. Christo­pher Colose, a post­doc­toral re­search fel­low at NASA GISS, puts it clearly:

Ac­tual num­bers are im­por­tant here. The global tem­per­a­ture in­crease could in­deed reach 4-5 de­grees by 2100, if hu­mans don’t do any­thing to our emis­sions, and be­yond this patches of un­in­hab­it­able ar­eas (for hu­mans) could start to open up in the trop­ics, due to heat stress limits im­posed by the evap­o­ra­tive limits of our body. In­deed, a world 5+ de­grees warmer is a big cause for alarm, even if the world takes a lin­ear path to that mark. The world also does not end in 2100, and while it is tempt­ing to think of later dates as “very far off,” it is worth re­mind­ing our­selves that we would live on a differ­ent planet had peo­ple of the Vik­ing era in­dus­tri­al­ized and emit­ted car­bon un­con­trol­lably.
Nonethe­less, the near fu­ture cli­matic fate of New York prob­a­bly looks more like the cli­mate of South Carolina or Ge­or­gia than some­thing from a Mad Max movie. This is still an im­por­tant ba­sis for con­cern given that the so­cio-poli­ti­cal in­fras­truc­ture that ex­ists around the world is bi­ased to­ward the mod­ern cli­mate.
Many of the night­mare sce­nar­ios in this ar­ti­cle, such as no more food, un­breath­able air, poi­soned oceans, per­pet­ual war­fare, etc. are sim­ply ridicu­lous, al­though food se­cu­rity is in­deed an is­sue at stake (see David Bat­tisti’s com­ments). A “busi­ness-as-usual” cli­mate in 1-2 cen­turies still looks markedly differ­ent than the cur­rent one, but there’s no rea­son yet to think much of the world will be­come un­in­hab­it­able or look like a sci­ence fic­tion novel.

The IPCC, the world’s lead­ing ex­perts on cli­mate change, pub­lish reg­u­lar re­ports about cli­mate change which ex­plain what the ex­pert con­sen­sus about cli­mate change is. The most re­cent re­port about the im­pacts of cli­mate change was pub­lished in 2014. (The fifth as­sess­ment re­port is in drafts but has not been offi­cially pub­lished.) It lists five rea­sons for con­cern about cli­mate change:

  1. Unique and threat­ened sys­tems— Cli­mate change will de­stroy cer­tain vuln­er­a­ble cul­tures and ecosys­tems.

  2. Ex­treme weather events— Cli­mate change in­creases the risk of some nat­u­ral dis­asters, such as heat waves, coastal flood­ing, and ex­treme amounts of rain.

  3. Distri­bu­tion of im­pacts— Cli­mate change will dis­pro­por­tionately harm the global poor.

  4. Global ag­gre­gate im­pacts— Due to cli­mate change, we’ll have a harder time get­ting the things we usu­ally get from na­ture– pol­li­na­tion, flood con­trol, bush­meat, and so on– which will harm the econ­omy.

  5. Large-scale sin­gu­lar events— Some phys­i­cal sys­tems and ecosys­tems are at risk of abrupt and ir­re­versible changes, such as the loss of the Green­land ice sheet.

Key risks are the po­ten­tially se­vere ad­verse con­se­quences for hu­mans re­sult­ing from cli­mate change. The list of key risks is as fol­lows:

i) Risk of death, in­jury, ill-health, or dis­rupted liveli­hoods in low-ly­ing coastal zones and small is­land de­vel­op­ing states and other small is­lands, due to storm surges, coastal flood­ing, and sea level rise. [RFC 1-5]
ii) Risk of se­vere ill-health and dis­rupted liveli­hoods for large ur­ban pop­u­la­tions due to in­land flood­ing in some re­gions. [RFC 2 and 3]
iii) Sys­temic risks due to ex­treme weather events lead­ing to break­down of in­fras­truc­ture net­works and crit­i­cal ser­vices such as elec­tric­ity, wa­ter sup­ply, and health and emer­gency ser­vices. [RFC 2-4]
iv) Risk of mor­tal­ity and mor­bidity dur­ing pe­ri­ods of ex­treme heat, par­tic­u­larly for vuln­er­a­ble ur­ban pop­u­la­tions and those work­ing out­doors in ur­ban or ru­ral ar­eas. [RFC 2 and 3]
v) Risk of food in­se­cu­rity and the break­down of food sys­tems linked to warm­ing, drought, flood­ing, and pre­cip­i­ta­tion vari­abil­ity and ex­tremes, par­tic­u­larly for poorer pop­u­la­tions in ur­ban and ru­ral set­tings. [RFC 2-4]
vi) Risk of loss of ru­ral liveli­hoods and in­come due to in­suffi­cient ac­cess to drink­ing and ir­ri­ga­tion wa­ter and re­duced agri­cul­tural pro­duc­tivity, par­tic­u­larly for farm­ers and pas­toral­ists with min­i­mal cap­i­tal in semi-arid re­gions. [RFC 2 and 3]
vii) Risk of loss of marine and coastal ecosys­tems, bio­di­ver­sity, and the ecosys­tem goods, func­tions, and ser­vices they provide for coastal liveli­hoods, es­pe­cially for fish­ing com­mu­ni­ties in the trop­ics and the Arc­tic. [RFC 1, 2, and 4]
viii) Risk of loss of ter­res­trial and in­land wa­ter ecosys­tems, bio­di­ver­sity, and the ecosys­tem goods, func­tions, and ser­vices they provide for liveli­hoods. [RFC 1, 3, and 4]

To be clear, all of this is re­ally bad. Peo­ple are go­ing to die. “Eco­nomic dam­age” sounds dry and ab­stract, but it means peo­ple go­ing hun­gry and chil­dren dy­ing of pre­ventable dis­eases. The effects will fall sub­stan­tially on the global poor, who have limited re­sources to help them cope. We can ex­pect a cli­mate re­fugee crisis.

It is also, no­tably, not hu­man ex­tinc­tion.

Hu­man ex­tinc­tion, if it were a likely out­come of cli­mate change, would prob­a­bly fall un­der rea­sons for con­cern #4 or #5 (al­though it’s still weird it didn’t get its own head­lin­ing con­cern). For this rea­son I will dis­cuss #4 and #5 in more depth.

There is a low level of con­sen­sus about con­cern #4. If global warm­ing is kept be­low 3 de­grees Cel­sius, 20 to 30% of species are at risk of ex­tinc­tion– mostly spe­cial­ist species who would have a far more difficult time adapt­ing to cli­mate change than hu­mans would. Below 2.5 de­grees Cel­sius, cli­mate change will only cause a small re­duc­tion in gross world product; there is no con­sen­sus about the effects about 2.5 de­grees Cel­sius, but they are ex­pected to ac­cel­er­ate with in­creas­ing tem­per­a­ture. Hu­man ex­tinc­tion is nowhere listed as a po­ten­tial con­se­quence of ex­treme lev­els of warm­ing.

Con­cern #5 in­cludes the fol­low­ing large-scale sin­gu­lar events:

  • Over cen­turies or mil­len­nia, the Green­land ice sheet and pos­si­bly the West An­tar­tic ice sheet may deglaci­ate, lead­ing to a five to ten me­ter rise in sea level.

  • The dis­ap­pear­ance of the Arc­tic sum­mer sea ice, which is likely re­versible, al­though loss of bio­di­ver­sity is not.

  • Ir­re­versible changes in coral reef, Arc­tic, and Ama­zon ecosys­tems.

  • Two events de­scribed as “un­likely” or “very un­likely,” which in­clude:

    • Ac­cel­er­ated car­bon emis­sions from wet­lands, per­mafrost, or ocean hy­drates, which could cause a higher-than-pre­dicted rate of global warm­ing. I have not been able to find an es­ti­mate of how high the warm­ing would be or what the effects would be.

    • Shut­down of the At­lantic meri­dional over­turn­ing cir­cu­la­tion (AMOC), which would cause cool­ing in North Amer­ica and Europe, in­creased ex­treme weather events, and (no mat­ter what the Day After To­mor­row tells you) not hu­man extinction

One con­cern I’ve of­ten seen is an ac­cel­er­ated green­house effect turn­ing us into Venus. How­ever, Cli­mate Feed­back quotes Ken Caldeira, se­nior sci­en­tist at the Carnegie In­sti­tu­tion for Science:

The Earth is not at risk of be­com­ing like Venus. We have done cli­mate model simu­la­tions in which all available fos­sil fuels were burned and the re­sult­ing CO2 re­leased into the at­mo­sphere. The planet warmed up about 10 °C in these simu­la­tions. This was enough to melt all of the ice sheets and pro­duce 60 me­ters of sea-level rise, but in no such simu­la­tion does the Earth be­come any­thing like Venus.

Most of our cli­mate mod­els only ex­tend to the rel­a­tively near fu­ture, such as 2100. There is a high de­gree of un­cer­tainty about what will hap­pen in the more dis­tant fu­ture, with some ex­cep­tions, such as the melt­ing of the Green­land ice sheet. It’s difficult to model things that are that far away. No one re­ally knows what the world would look like in 2500 with three de­grees of warm­ing. But there’s also a lot of time in the next five hun­dred years to de­ploy other miti­ga­tion and adap­ta­tion solu­tions.

In con­clu­sion, cli­mate change will be very very bad. Lots of peo­ple will die. Many peo­ple– dis­pro­por­tionately the global poor– will go hun­gry, get sick or in­jured, not have ac­cess to clean wa­ter, or suffer from treat­able or pre­ventable ill­nesses. There will be many nat­u­ral dis­asters. There will be global geopoli­ti­cal in­sta­bil­ity, per­haps in­clud­ing wars and re­fugee crises. We will dam­age or lose many ecosys­tems that peo­ple value, such as coral reefs. The Ama­zon may be­come a grass­land. But sci­en­tific con­sen­sus is that it will not re­sult in hu­man ex­tinc­tion or Earth be­com­ing Venus.