Climate Change Throughout History PDF

#tle 1 Outline In red, the content of this powerpoint file 2 Outline 3 The etymology of "climate" - κλιµα in greek – means inclina#on (angle), in rela#on to the height of the sun above the horizon. Up to the 17th century, this word w...

#tle 1 Outline In red, the content of this powerpoint file 2 Outline 3 The etymology of "climate" - κλιµα in greek – means inclina#on (angle), in rela#on to the height of the sun above the horizon. Up to the 17th century, this word was oJen used as a synonymous of "geographic la#tude". The concept of "climate" is therefore originally a geographic one: climate is supposed to change with loca#on, but not with #me. The key idea is to define the environmental condi#ons for humans (... ie. the habitable zone). During the an#quity, Aristote defines the "habitable zone" on Earth as the la#tude bands between the tropics and the polar circles where temperatures are not too hot or too cold. Geographers will later classify and map more precisely "climates" as a func#on of temperature and precipita#on, the two main physical determinants for living organisms like us. But then, what is a "global clima#c change", like the one that we are currently experiencing ? If "climate" is clearly a no#on arising from geography (= human environment), "clima#c change" is not. Obviously there is here a strong seman#c shiJ that needs to be underlined. 4 The idea that the global Earth climate may change through #me arises from geology. The ini#al ques#on was the forma#on of the Earth (from "fire" according to the plutonist's theories) and it was usually assumed that Earth cooled progressively through #me. Accordingly, many (wrong) preconcep#ons on past Earth's climate are s#ll living today... as we will see later. This idea was used to compute the age of the Earth (linear extrapola#on of measured cannonball cooling #me from the molten state by Buffon 1755, or the more detailed computa#on of heat diffusion by Kelvin 1860). This led to a famous dispute in the end of the 19th century between physicists and geologists who were thinking the Earth should be several billion years old (based of sedimentary sequences). Physicists were wrong... 5 The discovery of ice ages changed completely the no#on of clima#c changes. It became obvious that climate is not determined by the cooling of the Earth: other mechanisms are required. Past temperatures could not be easily deduced from paleontology since fossil plants and animals were not necessarily comparable to today's ones. In contrast, ice ages are clearly iden#fied in the physical landscape in Europe or in North America: the only explana#on is a very large expansion of glaciers in a quite recent past. Stria#ons : show the direc#on of ice flow on long distances. "Roches moutonnées": rounded glacially-shaped rocks Moraines : hills composed of glacial debris at the edge of the glacier... 6 The discovery of ice ages Boulders, glacial erra#cs: large rocks (thousands of tons) that have been transported kilometers away by the glaciers down the valleys. 7 The discovery of ice ages changed completely the no#on of clima#c changes. It became obvious that climate is not determined by the cooling of the Earth: other mechanisms are required: 1 - climate is determined by the atmospheric composi#on, in par#cular in greenhouse gases. The greenhouse effect was already described by Fourier (1824): the atmosphere captures the "dark heat" (= infrared radia#on) depending on its composi#on, like its cloud cover for instance. Tyndall measured the IR radia#on absorbed by atmospheric gases: greenhouse gases are mostly the water vapour and carbon dioxide. Arrhenius (1896) did compute the clima#c effect of CO2... 2 - climate is determined by the changing astronomical parameters of the Earth. It was already known in the an#quity that there is a "3rd movement of the Earth" (precession of the equinoxes) while the 1st and 2nd movement (day and year) have clear clima#c consequences. 8 9 Arrhenius (1896) was the first to compute the clima#c effect of CO2. Callendar (1938) was the first to "detect" a warming in the observa#ons that was compa#ble with the increase in CO2 concentra#on. AJer the 1950s, there was some significant advances in the computa#on of atmospheric IR bands radia#on (thanks to military and avia#on technological development) as well as in compu#ng power. Manabe got the physic's Nobel prize in 2021. The Charney report (1979) is the first scien#fic assessment report for policymakers prepared at the request of the american government (J. Carter). Since the end of the 19th century, the global clima#c effect of a CO2 doubling (equilibrium climate sensi#vity ECS) has been re-evaluated using more and more sophis#cated models. Arrhenius' conclusion that CO2 has a significant effect on climate remains true. 10 Arrhenius' conclusion that CO2 has a significant effect on climate remains true. Global warming was clearly presented on american educa#onal TV programs in the 1950's more than 60 years ago. Global warming is not a new finding... 11 Global warming was predicted in the 19th century and was computed in the 20th century. The new thing in the 21st century is that it is now quite clear also in the observa#ons. In 2022: a global warming of about +1°C (compared to 1950-1980) but more on lands (were we live): +1,4°C than at the oceans' surface: +0,65°C Less heat capacity on land (heat diffusion in the ground is very slow) More heat capacity over the oceans (mixing of the top 50m or more by winds). 12 How does this compares to past global changes ? Beware the non-linear #me-scale, from the Cambrian (540 millions years ago) to today. - In yellow - Paleozoïc + Mesozoïc periods: Quite indirect informa#on: mostly CO2 proxies, compa#ble with other geologic data. - In green + black - Cenozoïc period: Oxygen isotopic composi#on of (mostly?) benthic foraminifera : rather quan#ta#ve proxy of the ocean temperature + ice volume. - In blue – Quaternary period: Oxygen isotopic from ice cores (Antarc#ca and Greenland) : rather quan#ta#ve proxy of the air temperature above polar regions (rescaled). The Antarc#ca ice-sheet appears about 34 million years ago. The Greenland + other northern hemisphere ice-sheets appear about 3 million years ago. 13 Outline 14 How does this compares to past global changes ? The Eocene was quite warm... = warmest period of the Cenozoïc. 15 The Eocene was quite warm... = warmest period of the Cenozoïc. Polar regions experienced a tropical climate... palm trees, crocodiles,... even during the polar night ! 16 The Eocene was quite warm... = warmest period of the Cenozoïc. The CO2 was probably in the 1000-2000 ppm range (4xCO2 to 8xCO2). The CO2 drop 34 million years ago led to the building of Antarc#ca. There are many proxies for CO2, with some discrepancies. eg: Stomata : the density of stomata on fossil leaves can be related to CO2 (less CO2 requires more stomata for photosynthesis). Climate models have difficul#es to get "palm tress" or to melt Antarc#ca at these levels (4xCO2 to 8xCO2): - Models might not be sensi#ve enough? - Or CO2 was much higher ? - Or something else was involved ? 17 Carboniferous: cold or warm ? 18 Carboniferous: cold !! In contrast to what people thought in the 19th century, the CO2 was low at that #me. This corresponds to a rather severe glacia#on, las#ng tens of millions of years. 19 Carboniferous: CO2 was low at that #me. This is easy to understand if we assume that carbon is buried significantly (forma#on of coal deposits) while other fluxes might remain more or less unchanged. If carbon sinks increase, then atmospheric CO2 should decrease. This is the exact reverse situa#on compared to today since we are now burning the coal buried at that #me (and others). 20 Carboniferous: CO2 was low at that #me. There was indeed a tropical forest... close to the equator (like today and like always) due to the atmospheric circula#on. The largest con#nent in the Southern hemisphere (Gondwana) was mostly covered with a huge ice-sheet. Europe, Northern America, (part of) Russia and China where at the equator, therefore they could enjoy an industrial revolu#on based on coal 300 million years later. 21 The Phanerozoïc (= Paleozoïc + Mesozoïc + Cenozoïc) corresponds only to the last 540 million years. During the preceding 4 billion years, many climate changes did probably occur... The most spectacular ones are the "snowball Earth" periods, during which the Earth was almost en#rely covered with ice. - There were ice-sheets at the equator (glacial deposits,...) - The ocean became anoxic (was cover with ice). -... These events are well documented at 2 periods: about 750-700 million years ago and about 2.3 billion years ago. In conjunc#on with these 2 events, the oxygen on Earth rose considerably: The first event (2.3 billion years ago) correspond to the Great Oxyda#on Event. 22 Outline 23 Since the 19th century, the last glacial maximum is the best example we have of a very "different climate" at a recent #me period, for which we have a wealth of informa#on. The temperature was about 4 to 6°C colder, an amplitude of change comparable to what we expect at the end of the 21st century (but with the opposite sign). 24 The last glacial maximum. What is on this picture ? 25 The last glacial maximum : about 21 000 years ago. Great auks (Pinguinus impennis) - birds which lived in cold areas of the North Atlan#c up to the mid 19th century. The cave is situated in Marseilles (south of France) in the Calanques. The only entrance is 37 meters below sea-level. The pain#ngs are between 27 000 and 19 000 years old. - it was colder... See also Mammoths in many other paleolithic caves.. - the sea level was lower, by about 120 or 130 meters. 26 The last glacial maximum : about 21 000 years ago. The northern hemisphere was quite different: Canada was covered with ice, just like Scandinavia. Sea-level was lower: - The Bering strait is then the Bering Isthmus. - UK is part of Europe !!. - Indonesia is a true con#nent (Sunda), not a collec#on of islands. - There is no East China Sea anymore. 27 The last glacial maximum : about 21 000 years ago.... There is no North Sea anymore but an area called Doggerland. Actually, people lived there, as asested by archeological remains. 28 What is an ice-sheet? Antarc#ca today: About 2 to 4 km of ice thickness. Hundreds or thousands of kilometers wide. Not to be confused with sea-ice (typically 1 meter thick, made of sea water). It is grounded on a con#nent = inlandsis. It is made of freshwater (snow) accumulated during thousands of years. The top of Antarc#ca is the coldest place on Earth (average -55°C) It is the driest place (about 2 cm / year of precipita#on), but also the largest reservoir of freshwater (70% of Earth's freshwater). The bedrock can be below sea-level. An important feature is then the grounding line: the posi#on between grounded ice and floa#ng ice. When the ice is floa#ng on the ocean, the surface becomes very flat: this is an ice- shelf (in color in the right upper figure): the largest ice-shelves (Ross, Ronne-Filchner) are about the size of a large european country (France = 543 000 km2). When they break apart, they form icebergs that will melt further away in the ocean. 29 What is an ice-sheet? Antarc#ca today: The mass balance of the ice-sheet is linked to precipita#ons (snow accumula#on), atmospheric temperature (mel#ng, sublima#on) but also linked to ocean temperature (mel#ng below ice-shelves). The shape of the ice-sheet is largely controlled by the dynamics of the ice: ice is flowing from the center towards the sides of the ice-sheet (gravity, pressure, deforma#on). These flows mostly occurs in "small" well-defined streams (photo) that are kilometric in size (= valleys in mountains). The dynamics of an ice-sheet is largely controlled by small-scale topographic features... 30 Benthic d18O: a proxy of ice volume (ice sheet size, or sea level). deltaD: a proxy of Antarc#ca temperature. CO2, CH4, N2O : greenhouse gases concentra#ons (measured in the Epica DomeC ice core, but well-mixed in the atmosphere) Ice ages are linked both to astronomy and to greenhouse levels. The pacing is astronomical, with a main periodicity around 100 000 years, linked ("in some way" = not quite understood way) to the eccentricity of the Earth. A key (unsolved) problem is to understand what caused such large CO2 varia#ons and how it explains the ice age dynamics. 31 Dansgaard-Oeschger events. Ice cores from Greenland are showing an unexpected variability during ice ages: the averaged temperature can jump by 10° to 16°C in a maser of years or decades from cold to warm, and back to cold glacial temperature in a maser of decades or centuries. This led to the new no#on of "clima#c surprise" (IPCC 2001) : small changes may some#mes have large consequences... There are "#pping points" in the climate system. This was not really expected before this observa#on. 32 Heinrich events. Marine sediment cores from the North Atlan#c are showing abrupt episodes of iceberg discharges between 40° and 55°N : a lot of ice raJed debris, colder temperatures, less salty waters,... Part of the Lauren#de ice-sheet did "collapse" rather abruptly ! 33 The abrupt temperature changes in the North Atlan#c are likely linked to abrupt reorganiza#ons of the ocean circula#on. Today, the Atlan#c ocean transports heat from the Southern hemisphere to the Northern one (in contrast to other ocean basins, and in contrast to the atmosphere, which transport heat mostly from equator to pole) When this Atlan#c heat transport is stopped or reversed, the Northern hemisphere is cooled while the Southern hemisphere is warmed. This is precisely what is observed in ice cores from Greenland (GRIP) and Antarc#ca (Byrd and Vostok). This strongly suggest that abrupt clima#c changes during the last glacial period are linked to abrupt changes in ocean circula#on. It is s#ll not clear today what are the causes of these oceanic changes. 34 The abrupt temperature changes in the North Atlan#c are likely linked to abrupt reorganiza#ons of the ocean circula#on. Indeed the ocean can switch abruptly from one state to the other. This is the subject of the following tutorial session. 35 36 A short summary of Planck's law (back body radia#on) - derived from sta#s#cal physics Two important consequences: - the integral over the whole spectrum is simply = sigma T^4 - the wavelength corresponding to the maximum power density is given by Wien's displacement law. 37 Radia#ve balance of an isothermal sphere (+ rapidly rota#ng) illuminated from one side. The temperature can be easily computed from the incoming radia#on (solar constant) and the albedo, using Planck's law of black-body radia#on. When averaged over the Earth's surface, the solar incoming radia#on (solar constant) is divided by 4 due to geometry. 38 The radia#ve balance of an isothermal sphere: when applied to other planets, this simple rela#on gives a good approxima#on of "surface temperature" when there is no (or almost no) atmosphere. On Venus, it fails drama#cally... Something is missing : the greenhouse effect. 39 But what is THE temperature we are looking for in clima#c studies ? The figure shows a schema#c of the ver#cal temperature profiles in the atmosphere (blue) in the ocean (red) and in the solid Earth (orange). - is it the "averaged" temperature of the atmosphere ? of the ocean ? - is it the "surface" temperature at ground level ? -... 40 Something to keep in mind: climate is a very anthropocentric concept, defined by and for geographers. The temperature of interest is therefore the one we are measuring in standardized white boxes at 1,5 meters above the surface, "where we live" and where we put the thermometer. From a physical point of view, this is probably not the best place to measure something like "the temperature of the Earth"... 41 From a physical point of view, the "atmospheric surface" (or at 1,5 meters) is probably not the best place to measure something like "the temperature of the Earth"... A more relevant place could be the ocean, since this is where the heat accumulates. On the figure : heat accumula#on over the past decades. The mass of the ocean is about 300 #mes larger than the mass of the atmosphere. The specific heat capacity of water is about 4 #mes larger than the one of air. The overall heat capacity of the ocean is therefore 1000 #mes larger than the one of the atmosphere : a global clima#c change is therefore more reliably recorded in the ocean. Note: concerning past climates, the paleo-temperatures are oJen obtained from oceanic data. 42 What is this planet ? 43 From a physical point of view, the "atmospheric surface" (or at 1,5 meters) is probably not the best place to measure something like "the temperature of the Earth"... Astrophysical objects emit radia#on to space and it is usual to measure the temperature of this radia#on (according to Wien's displacement law), just like when using any infrared thermometer. Blue stars are hoser than red stars. The Sun's surface temperature is about 6000K... And the Earth's temperature is about 255K, ie. the temperature Te that we computed before. This is another physically sound measure of temperature... We can also state that this image is quan#ta#vely more correct than the standard "blue planet" picture we are used to see: it represents about 235 W.m-2 while visible light accounts for 107 W.m-2. In terms of energy, this picture weighs twice as much as the standard "blue planet" one. In terms of photons, this is even more true... 44 The greenhouse effect correspond to a situa#on were radia#on is emised at a colder temperature (than the one we are interested in = the surface). This is linked to the temperature gradient in the atmosphere, which gets colder higher in the troposphere. More precisely, the lower levels of the atmosphere are opaque in the IR frequency domain while the upper tropospheric levels are much more transparent in the IR. This is mainly due to water vapour which is present only in the lower levels. At high al#tude, it is very cold and most of the water vapour is removed by condensa#on (precipita#on). The upper troposphere (the tropopause) acts as a "cold trap" for water. (This forbids water from escaping... water vapour is the stratosphere is dissociated into oxygen + hydrogen, and hydrogen can escape gravity. Without this cold trap, there would be rapidly no more water on Earth...) The role of each greenhouse gas can be seen on the figure (with absorp#on bands as 45 The main heat fluxes at radia#ve equilibrium in the atmosphere.... to be examined in more details during the tutorial session. When the greenhouse gas concentra#on increases, the exchanges between the lower and upper troposphere are increased (surface radia#on, back radia#on). When reaching a new (warmer) equilibrium, the solar radia#on and outgoing radia#on may remain constant (if the albedo is unchanged), but the inner fluxes (and the surface temperature) will remain higher that in the previous equilibrium. 46 Assuming a constant "greenhouse effect coefficient" epsilon = 0,4 and assuming a simple piecewise linear or constant rela#onship between albedo and temperature to account for ice (mostly sea-ice), we easily get an interes#ng non-trivial result : - there are 3 possible equilibria : actually only 2 since the middle one is unstable. - there is an hystéresis when changing (for instance) the greenhouse parameter: when lowering it below a given threshold, there is only one possible equilibrium (very cold!) and in the same way when increasing it above another threshold (very hot!). - The situa#on is mathema#cally similar to the previous tutorial session where we had mul#ple equilibria of the ocean circula#on. - This is the basis for the "snowball" episode during Proterozoïc #mes (750 and 2300 millions years ago) : easy to get in, more difficult to get out. 47 outline 48 Seasons are the most obvious clima#c phenomena. The first clima#c discovery is the inven#on of the calendar and the origin of astronomical science thousands of years ago, to predict the return of seasons. Climate can be defined as "the predictable part" of the system, just like seasons are predictable. Seasons are linked to the obliquity of the Earth axis (epsilon) versus the eclip#c (the orbital plane). This defines the tropics and the polar circles : in the tropics the Sun is at the zenith twice a year; beyond the polar circles, the Sun may not rise or set. 49 The incoming solar radia#on (short wave radia#on) depends therefore both on la#tude and of the #me of the year (month or season). This can be easily computed with elementary trigonometry, knowing obliquity, eccentricity and clima#c precession (rela#ve posi#on of seasons and perihelion) - summer = maximum incoming radia#on : 21st june in the north; 21st december in the south - maxima at the poles at the sols#ce : the length of the day is important !! - sols#ce maximum stronger at the south pole (coldest place on Earth!) because we are closer to the Sun around january 4th (perihelion)... 50 The seasonal changes in temperature are linked to 2 main factors: the height of the Sun above the horizon and the length of the day. For instance, at our la#tude, they have both the same role in summer while the low height of the Sun is more important in winter to account for cold temperatures. The length of the day has a dominant role at higher la#tudes. 51 But obliquity changes through #me... together with the tropics and polar circles. Varia#ons are between about 22° and 24,5° with a 41 000 year periodicity... 52 Anima#on Evolu#on of incoming solar radia#on (func#on of month and la#tude) with a #me evolu#on taken at the june sols#ce at 65°N, where ice-sheets may change during the Quaternary #me period. 53 These varia#ons have a cri#cal role in the dynamics of ice-sheets for glacial- interglacial changes. In par#cular, the northern hemisphere ice sheets grow to their maximum when the insola#on forcing remains low for an extended period of #me (black rectangles), then a deglacia#on occurs at the next insola#on maxima (for reasons not en#rely clear). 54 outline 55 Scheme of the carbon cycle. Numbers in black are the pre-industrial values for fluxes and reservoir sizes (red are the anthropogenic perturba#ons). The "Earth surface" reservoirs are (unperturbed values): - the ocean = 38000 GtC (gigatons of carbon) - the biosphere (+soil) = 2300 GtC - the atmosphere = 600 GtC There are strong exchanges between the atmosphere and vegeta#on, and also between the atmosphere and surface ocean. The atmosphere is the smallest reservoir : the fate of anthropogenic carbon depends on the capacity of the vegeta#on and ocean to take up carbon. 56 Over the past, the atmosphere has accumulated only half of the carbon emised by human ac#vi#es. The other half was stored in the vegeta#on and in the ocean. It is not clear whether they can absorb this propor#on of our emissions in the future and data suggest that the ocean may progressively saturate. Vegeta#on may also be affected by climate change in the future and could have more difficul#es to store carbon. 57 On longer #me scales atmospheric CO2 in largely controlled by the chemistry of the ocean (the largest reservoir). CO2 is an acid : it dissociates into HCO3- (hydrogeno-carbonate ions) and CO3= (carbonate ions). Adding CO2 from the atmosphere lowers the pH. Ocean pH has already been lowered by about 0.1 pH unit due to anthropogenic carbon. pH of the ocean is about 8,2 (pK1 is about 6 and pK2 is about 9) therefore most of the carbon in the ocean is HCO3- (about 90%) and also CO3= (about 10%) : the atmosphere only "sees" the dissolved H2CO3 which is a small part of the oceanic carbon. The behaviour of oceanic carbon depends on two main variables: total dissolved (inorganic) carbon C and total alkalinity A. Alkalinity can be understood as the sum of electric charges of weak acids: as a conserved quan#ty it is useful to establish balance equa#ons. Adding CO2 from the atmosphere lowers the carbonate content [CO3= ] and therefore dissolves calcareous rocks (shells, coral reefs,...). On the long term (thousands of years), this dissolu#on may restore the carbonate content [CO3= ] : this is called the carbonate compensa#on. 58 The carbonate chemistry of the ocean depends (mostly) of the 2 variables C (total dissolved inorganic carbon) and A (alkalinity). The carbonate concentra#ons varies with A-C (increases with A, decreases with C) The equilibrium pCO2 does almost the opposite (decreases with A, increases with C), but with a slightly different slope.. 59 The carbonate chemistry of the ocean depends (mostly) of the 2 variables C (total dissolved inorganic carbon) and A (alkalinity). The carbonate concentra#ons varies with A-C (increases with A, decreases with C) The equilibrium pCO2 does almost the opposite (decreases with A, increases with C), but with a slightly different slope. This different slope has consequences: 1- The injec#on of CO2 increases C (decreases pH, decreases carbonates, therefore dissolves carbonate rocks). 2- The dissolu#on of carbonates increases both A and C (in a 2 to 1 ra#o) up to restoring carbonate ions (assuming for instance that calcium is constant... but also that the ocean is a simple well-mixed box...). But even aJer this carbonate compensa#on, the pCO2 remains higher than before (the pCO2 isolines are steeper). In order to restore climate to ini#al state, we need a last step: 3 – silicate weathering of mountains uses atmospheric CO2 as an acid and neutralized it on a rock, bringing HCO3- ions into the sea through rivers. The net effect is to add alkalinity without changing the total carbon of the ocean-atmosphere system. 4 – this can be compensated by carbonate precipita#on. 60 An interes#ng example: the Paleocene-Eocene transi#on. An abrupt warming = a geological trans#on. 61 An interes#ng example: the Paleocene-Eocene transi#on. - Decrease of carbon 13 = massive injec#on of carbon with low 13C content (fossil organic, gas, clathrates..) A possible candidate are methane hydrates (clathrates): a mix of water ice with methane, stable only for specific T and P condi#ons, that is abundant on con#nental shelves and may be destabilized by long-term warming (Paleocene trend) or sea-level changes, or... - Increase of temperature by about 5 °C This is a likely consequence of a massive carbon injec#on... - Complete stop of carbonate precipita#on. This is a also likely consequence of a massive carbon injec#on... Things get back to "normal" aJer about 200 000 years, probably thanks to silicate weathering ? 62 Silicate weathering is possibly THE main mechanism stabilizing climate: - over geologic #mes the main carbon fluxes are volcanic inputs, burial of organic maser, and carbonates precipita#on - volcanic inputs are unlikely to depend on climate or Earth surface carbon concentra#ons. - burial of organic maser is likely to depend on climate and carbon concentra#ons but in a complex and not well understood fashion. - carbonates precipita#on depends (rather) simply on silicate weathering, which depends on climate, which depends on carbon. If we assume that weathering increases when pCO2 increase (for several reasons, but mainly because of increased precipita#on), then we have a very strong nega#ve feedback: climate is regulated to stay in a regime with ac#ve run-off 63 Silicate weathering is possibly THE main mechanism stabilizing climate: Proxies of past pCO2 (to be taken with cau#on...) suggest a decreasing trend over the last 500 million years that compensates for an increase in the solar constant. (the Sun gets brighter through its long term evolu#on, like all stars). With increased solar radia#on, weathering becomes more efficient thus lowering CO2 to get the same fluxes to equilibrate volcanic inputs. 64 In the far future (1 billion years) CO2 will get vanishingly low and cannot compensate for a brighter Sun. When this thermostat is broken, the Earth gets very hot (run-away greenhouse like Venus) and looses its water (the tropopause cold trap also breaks down). 65 In the less far future (1 million years) anthropogenic CO2 will slowly decrease thanks to silicate weathering and glacial cycles may start again at some point (in 600 000 years, 800 000 years), depending on our emissions now... 66 In the less less far future (thousand years) anthropogenic CO2 will keep the Earth warm and will induce sea-level rise (it takes thousands of years to equilibrate thermally the deep ocean) and ice-sheet mel#ng (it also takes thousands of years to melt Greenland or parts of Antarc#ca). There are only few studies on this not so far #me scale, and the response of ice- sheets remains uncertain. 67 As you know... this is due to our emissions that keep increasing... 68 Emissions keep increasing since we are using always more and more fossil fuels... The increase in fossil fuels over the last 20 years is FAR larger than the increase in carbon-free energies. 69 70