Yesterday, I posted a press release on a paper that suggested soil was going to accelerate global warming. Now today, we have the opposite; “Soil holds potential to slow global warming”.
Collectively, I don’t think climate science has a clue either way.
Climate solution in soil?
Soil holds potential to slow global warming, Stanford researchers find
STANFORD UNIVERSITY
If you want to do something about global warming, look under your feet. Managed well, soil’s ability to trap carbon dioxide is potentially much greater than previously estimated, according to Stanford researchers who claim the resource could “significantly” offset increasing global emissions. They call for a reversal of federal cutbacks to related research programs to learn more about this valuable resource.
CREDIT Jennifer Harden
The work, published in two overlapping studies Oct. 5 in Annual Review of Ecology, Evolution and Systematics and Global Change Biology, emphasizes the need for more research into how soil – if managed well – could mitigate a rapidly changing climate.
“Dirt is not exciting to most people,” said earth system science professor Rob Jackson, lead author of the Annual Review of Ecology, Evolution and Systematics article and coauthor of the Global Change Biology paper. “But it is a no-risk climate solution with big cobenefits. Fostering soil health protects food security and builds resilience to droughts, floods and urbanization.”
Humble, yet mighty
Organic matter in soil, such as decomposing plant and animal residues, stores more carbon than do plants and the atmosphere combined. Unfortunately, the carbon in soil has been widely lost or degraded through land use changes and unsustainable forest and agricultural practices, fires, nitrogen deposition and other human activities. The greatest near-term threat comes from thawing permafrost in Earth’s northern reaches, which could release massive amounts of carbon into the atmosphere.
Despite these risks, there is also great promise, according to Jackson and Jennifer Harden, a visiting scholar in Stanford’s School of Earth, Energy & Environmental Sciences and lead author of the Global Change Biology paper.
Improving how the land is managed could increase soil’s carbon storage enough to offset future carbon emissions from thawing permafrost, the researchers find. Among the possible approaches: reduced tillage, year-round livestock forage and compost application. Planting more perennial crops, instead of annuals, could store more carbon and to reduce erosion by allowing roots to reach deeper into the ground.
Jackson, Harden and their colleagues also found that about 70 percent of all sequestered carbon in the top meter of soil is in lands directly affected by agriculture, grazing or forest management – an amount that surprised the authors.
“I think if beer bets were involved, we all would have lost,” Harden said of her coauthors.
Jackson and his coauthors found a number of other surprises in their analysis. For example, plant roots are ?ve times more likely than leaves to turn into soil organic matter for the same mass of material. The study also provides the most complete estimate yet of carbon in peatland and permafrost – almost half of the world’s estimated soil carbon.
“Retaining and restoring soil organic matter helps farmers grow better crops, purifies our water and keeps the atmosphere cleaner,” said Jackson, Michelle and Kevin Douglas Provostial Professor in the School of Earth, Energy & Environmental Sciences.
Overcoming obstacles
The Jackson-led study describes an unexpectedly large stock of potentially vulnerable carbon in the northern taiga, an ecosystem that is warming more rapidly than any other. These carbon stocks are comparatively poorly mapped and understood.
The study warns of another danger: overestimating how the organic matter in soil is distributed. Jackson and his coauthors calculate there may be 25-30 percent less than currently estimated due to constraints from bedrock, a factor previously not analyzed in published scientific research.
While scientists are now able to remotely map and monitor environmental changes on Earth’s surface, they still don’t have a strong understanding of the interactions among biological, chemical and physical processes regulating carbon in soils. This knowledge is critical to understanding and predicting how the carbon cycle will respond to changes in the ecosystem, increasing food production and safeguarding natural services we depend on, such as crop pollination and underground water storage.
A rapidly changing climate – and its effects on soil – make these scientific advances all the more urgent.
“Soil has changed under our feet,” Harden said. “We can’t use the soil maps made 80 years ago and expect to find the same answers.”
However, funding pressures such as federal cuts to climate science, combined with turnover in science staff and a lack of systematic data threaten progress on soil carbon research. Jackson, Harden and their colleagues call for a renewed push to gather significantly more data on carbon in the soil and learn more about the role it plays in sequestering carbon. They envision an open, shared network for use by farmers, ranchers and other land managers as well as policymakers and organizations that need good data to inform land investments and conservation.
“If we lose momentum on carbon research, it will stifle our momentum for solving both climate and land sustainability problems,” Harden said.
###
Feynman covered this:
You can never prove a vague theory wrong.
Actually I think it was Satan who got the gravy train rolling with his offer of ‘Free Apples for All’. Who could resist that at the time?. In other words ‘climate science; is not ‘science’ with actual theories, reasonable, speculative, vague or just plain false, it is a marketing campaign designed to give power to the agents and activators of the campaign The propositions that soil is the device of Gaia/Satan are equally plausible in that sense and it is just getting the delivery right is where the focus is placed.
Let me guess, the remedy for the straw-man soil argument is active management with lots of tax credits involved and warnings of more funding needed instead of just suggested.
Straw man? Straw is the stems of grassy plants like wheat and oats. Makes great mulch for seeded areas. Also, when plowed under, it aerates the soil it’s been sitting on.
“They call for a reversal of federal cutbacks to related research programs to learn more about this valuable resource.”
If you give us more money….I’m sure we can save the world
Yet another argument that becomes moot considering the actual sensitivity to increasing CO2 concentrations.
That fits the warmist narrative – “Everything causes global warming, and global warming causes everything.”
… the debate is over, let the dueling start…
Climatechangepredictions has a good list on opposites caused by climate change, many of them found in scientific literature no prob. It’s funny, but they actually can find a theology to explain it out.
Here in OZ we call it having a bit each way , looks like they’re just covering all bases .
Having played on the close periphery of the agriculture, forestry and land management industries in my state I have known more than a couple of soil scientists and if I remember an entire university program on the subject. As powerful and agriculture and forestry are in the US I cannot imagine proper and appropriate funding being cut far enough to have an adverse impact. My guess is these researchers want to join their CAGW buddies and coming up with “science” to back more government regulations on land use. One of the longest held desires of the organized environmental movement is for government to have TOTAL control over land. They HATE the idea of private property rights.
“Planting more perennial crops, instead of annuals, could store more carbon and to reduce erosion”
Yeah, good idea, we can do the perennial thing, like all those perennial varieties of corn, rice, and wheat
Actually, perennial fed beef is much more tasty than non-perennial fed. More perennials!
So more coffee.
I remember an author who quoted “The best way to remove CO2 from the atmosphere is to tar a road or build a library”.
They may be scientists but they sure aare not farmers or foresters, who know these things intuitively up close and personal.
Anyone who has ever lived near a forest (my house backs into one) knows that duff – the partially decayed leaf matter on the forest floor – does not magically oxidize into CO2 every year, but instead grows deeper and deeper with each passing year. If you dig into a forest floor you can find duff extending down two or three feet in places. On a worldwide basis this constitutes an enormous carbon store.
Of course, if someone would like to fund me to the tune of a few million dollars I will happily go out and make a few measurements and publish them.
Roger Graves – October 7, 2017 at 7:48 am
Roger, ……. Roger, …… Roger, …… now why in the world would you want to post such a dastardly false statement about the yearly microbial decomposition of dead biomass, ….. when everyone knows for a fact, …… especially the “wannabe” and the “expert” climate scientists, …… that it is the “wintertime” microbial decomposition of all of that dead biomass in the Northern Hemisphere that is responsible for the September to mid-May increase of an average 8 ppm in atmospheric CO2 ….. as per the 59 years of the Mauna Loa CO2 Record stipulates.
Yours Truly, …… Eritas Rabuf
These scientists all have dirt for brains, heavily manured dirt for brains.
I agree with the modification of no dirt included for their brains, just 100% bull-s_ _ _!!
The carbon cycle is poorly understood. In spite of that, ‘they’ do the carbon budget to three or four significant digits. example
‘They’ attribute the rise in CO2 to anthropogenic emissions. Balderdash. If you change any of dozens of carbon sinks and sources by a single percent, you would get the same effect.
I agree that more research is needed to understand the carbon cycle. On the other hand, given the current zeitgeist I would say that money spent on that research would be wasted. It’s almost certain that the results of any research would conform to the party line.
In other words, we need the research but there’s precious little chance it would be done honestly.
..As evidenced by the lines: A rapidly changing climate – and its effects on soil – make these scientific advances all the more urgent.
…Send money now!
“Hi. We’re government bureaucrats, and we’re here to tell you how to better manage your lands, what to grow, etc. Don’t worry! We know more about this than you do, and besides, it’s to help save the planet. You want to help save the planet, right?”
The only farming these Stanford rent seekers have ever done is within the federal grant programs!
Cut the funding…. and you cut the ‘climate and land sustainability problems’ crap.
Federal cuts to climate science? When did that happen?
Obama did that? Wow.
From the article:
1. Unfortunately, the carbon in soil has been widely lost or degraded through land use changes and unsustainable forest and agricultural practices, fires, nitrogen deposition and other human activities.
2. Jackson, Harden and their colleagues also found that about 70 percent of all sequestered carbon in the top meter of soil is in lands directly affected by agriculture, grazing or forest management – an amount that surprised the authors.
Contradiction? The carbon in soil has been widely lost due to human activities, and 70% of all soil carbon is found in lands directly affected by human activities.
Once you have a contradiction, you can derive any conclusion.
At least they’re starting to reference the Carbon Cycle. That’s the cycle that can’t complete without Carbon Dioxide.
They would be correct but for one really rather large elephant.
Weathering. The erosion of trace yet vital nutrients from soils everywhere.
It is the same process that says a slate roof on your house is only really good for 100 years – that a cement-tile roof maybe 40 or 50.
Any and all rain, rain that falls through any atmosphere containing any amount of certain gases, (CO2, SO2, SO3 and NOx) becomes slightly acidic as a consequence and it dissolves/erodes the rock it lands upon.
If you have a problem with that, take it up with Old Ma Nature.
Plants depend on that and why else do the endless health yap yap yappies say:
eat this (it contains selenium for your diabetes)
eat that (it contains potassium for blood pressure)
eat the other (it makes your willie bigger)
etc etc
After millions and millions of years, the soil becomes depleted in these vital elements. They all finish up in the ocean and do not come back.
This is weathering and where we are now. Australia is massively old and weathered.
Likewise most of the US
Deserts by any name.
The plants don’t grow well.
How do you know?
So, Aussie farmers grow wheat and aare well chuffed at 1 tonne per acre
US farmers grow wheat and are ecstatic with 2 tonnes per acre (or some number of bushel feet acre inch perch rods that equal 2 tonnes)
English farmers grow wheat and if any one guy gets less than 4 tonnes per acre, he goes into hiding and everyone feels sorry for him.
The difference.
England was glaciated recently and the ice removed all the old weathered dirt and exposed new fresh rock.To some extent the same did happen across the US
Plants love that new rock
As these folks say, plants, alive and especially when dead & buried, control the immediate weather and hence the Climate. Simply via their control of water.
As I’ve said before, it appears totally crazy that thermometers say the place is warmer while huge amounts of extra energy are pouring out into space.
Simply nuts that higher temps indicate cooling – Real Cooling where there is less energy in the system.
And there-in is the HUGE problem with Climate Science, the relentless confusion of temperature with energy.
Consider a tropical rainforest. Temps stay at 23degC plus or minus 3deg across the ENTIRE year. Look at a desert at similar latitude and it swings 30 or 40 degrees on a daily basis and stores a fraction of the energy that the forest does.
Deserts may feel hot but they are actually very low energy (cold) places.
OK, my theory of Mars and where we’re all heading and why.
Photos and radar of Mars say that there was water there. There are beaches, cliffs, canyons, ravines and gullies, most of which cam only really have been created by water.
So where is it now?
The Faint Sun hypothesis, that life survived on Earth under a 25% weaker sun implies life (plants at least) could have, should have, existed on Mars.
And here’s the crunch, they would have weathered the soil.
Short of any huge volcanic events or epic meteor hits to create/expose fresh rock, the plants would have eventually starved and died.
Meanwhile soil microbes would continue to eat the dead organic material, making CO2 but most important, by drying the soil. (The old plant material acted as a sponge, same as here on Earth)
Mars would thus become a desert and hence go into an ice-age. It would become a planetary snowball – as Earth has done at least twice in its history.
Fortunately, something cracked Earth out of its snowball. Was it a huge meteor or some massive volcanism or combination of both?
Mars was not so lucky. Is Mars very volcanic (genuine question) but, as the solar system ages, the very large low-flying rocks are now small in number. Has Jupiter soaked them all up?
Again serious question, how magnetic is Mars. Not very I don’t think.
So, without a strong magnetic field, Mars would catch the full blast of the solar wind.
As we all know, if we have a home freezer at home, ice evaporates without melting.
So, Mars’ ice would sublimate, as ice does, and without a magnet to deflect the solar wind, the evaporated water would be blown away by said solar wind.
It eventually condensed further out where it is colder – onto bits of rock we sometimes see and call ‘comets’
We’ve been lucky on Earth. Escaped two snowball events and so, believe it or not, being repeatedly smacked by humongous rocks and epic volcanoes are major ‘strokes of luck’
Plus a strong magnetic field to catch any escaping ‘stuff’ and pump it back into the system at the poles.
So, call me misanthropic Malthusian pig-dog depressive Prince of Chuckles if it makes you feel better, but Mars is where we’re headed.
Agriculture, as we know and practice it, is weathering rock faster that it normally would and speeding our descend into what will become, a permanent ice age.
It was going to happen anyway, there are very few large boulders out there to crack the ice save us now.
Enjoy the ride while you can………..
I worry about the sun burning out…
“I worry about the sun burning out…”
Well, a man needs a hobby (:-))
The solar wind removing water fits perfectly -yes?
Its basically a distillation process and would leave the heavy stuff till last – surprise, that’s CO2.
Exactly what’s, and all, that is left of Mars’ atmosphere.
There are no links. I made it all up for you to take away and think about.
Stay off the grog and cut back on the doughnuts though, having a clear head does help with tailoring some REAL new clothes for our hapless Emperor, and by fook, is he gonna need them if I’m any where near right
Here’s a statistic for you, peta.
2015 total harvested wheat – all species:(red/white/hard/soft/winter/spring)
USA – 2,061,939,000.00 bushels
UK – 592,638,599.67 bushels
Looks like we outdid you by about 400%, and that was in a year with slumping market prices, too. We export a lot of grain crops. Much more than you do. In fact, UK imports wheat.
American farmers go by bushels per acre, regardless of the grain crop. The number of pounds per acre depends on the grain itself, as corn is obviously a larger grain than wheat or oats or soybeans.
Having owned a major dairy farm since 1985, the other and main reason we use volume rather than weight for crop yield (even boxes of fruits, with each fruit a different standard ‘box’) is weight depends on how dry the crop is when harvested. It is never the same year to year. In ‘wet’ harvest years we have to run propane heaters into the grain storage bins to dry down below 15% moisture to prevent rot and mold in corn, oats, soybeans. Country elevators will ‘steam’ for weeks. Whereas volume is roughly constant, even for alfalfa unless you change hay balers.
Gee, Peta, the last glacial maximum was the Wisconsin period, indicating that the southern border was Wisconsin. Before that, it was the Illinoisan. Before that, Kansas,and before that Nebraska. Lots of rock and soils were scraped and erratics moved around, drumlins and glacial kames left behind, moraines formed. I don’t know where in the blue-eyed world you get your information about what happened on the North American continent, but we do just fine. And your “tonnages” are inaccurate.
Um…Sara, he did say he made it all up. 🙂
Yeah, rocketscientist, but snarky snippets are sometimes ripe, y’know.
I guess ol’ Peta doesn’t realize that some time back in the billions of years ago, some Big Thing whacked Mars super hard and the entire magnetic core of Mars blew out onto the surface. It was in an old issue of Sky & Telescope – don’t remember which one – I read that the entire surface of Mars exhibits weak magnetism. And the Sun is slowly eroding Mars’ atmosphere, and at the same time, it seems to somehow be replenishing itself. Mars is a very weird little planet. And Elongated Musk wants to start a colony there.
I wonder if anyone with run into Gekko or any of the other real Martians some day. (Red Planet – Heinlein)
Mercury has a magnetic field, too, and a very thin atmosphere. And the moon is not made of Tang,after all.
Delusional fantasy peta.
Before Earth loses it’s atmosphere the Milky Way galaxy will collide with the Andromeda galaxy.
Whether Earth is tossed into space alone, pummeled by planetary debris or swept into the nuclear furnace of of a sun or black hole will be up to pure chance.
Not that anyone existing, including Hoboken peta, will even be around for the next glaciation.
That’s it. Proof that anyway you look at it, climate science is wrong.
I wouldn’t trust any scientist, that thinks thawing permafrost will lead to a net release of carbon into the atmosphere, to bag my groceries.
That’s a shocker. Soil scientists think we need to spend more on soil science.
I guess the science isn’t settled. If it were, why spend more money on climate research?
“Yesterday, I posted a press release on a paper that suggested soil was going to accelerate global warming.”
err no you didnt.
misreading the science and misrepresenting the science is not skepticism
What makes you say “err no you didn’t”, when our host obviously (see below) did?
Do you have a problem with the calendar or the interpretation of the articles. He did say “suggested” after all.
SteveT
Claim: The soil will turn on us and accelerate global warming
Anthony Watts / 1 day ago October 5, 2017
Carbon feedback from forest soils will accelerate global warming, 26-year study projects
It appears that these “researchers” are going after Dept of Agriculture money … knowing other dept monies are drying up.
Saying they are going to help “farmers, ranchers and other land managers as well as policymakers and organizations that need good data to inform land investments and conservation” creates a project that serves multiple concerns at the same time. Setting it up for grant requests.
Their being surprised that roots add to soil organics at a rate much higher than leaves shows that they don’t have the existing knowledge base that someone in their position should have. They were surprised at the 70% figure that they threw out. Maybe they are still surprised every time the clown pops out of the little metal box.
I don’t know whether to be annoyed at their ignorance of history and how it affects what’s in their cupboards and fridges, or just sit here and laugh at them.
Anyone who knows anything at all about botany knows that if you leave plant matter on the ground and plow it under or let it just decay for the next growing cycle, it returns nutrients to the soil, aerates it, and adds small layers of decaying matter that turn into more soil over time. In some places, midwestern prairie soil has been measured at up to six feet deep.
It use to be that farmers would clean up every bit of trash left in the fields after combining them, but that reduced the bushels per acre volume because the trash – e.g., straw, cornstalks, soybean or alfalfa roots – were what kept the soil aerated as well as preventing wind erosion in the winter. Remove that, and the soil becomes so fine-grained that plants can’t breathe and do poorly in it.
Rough tillage returned in the 1970s, and winter erosion stopped. Plowing last year’s “trash” into the soil aerated it as it was turned over, giving plant roots more room to spread and acquire more nutrients (water, fertilizer, soil minerals) for the plants to use for growth and production. The nutrients in the post-harvest ‘trash’ were returned to the soil.
I have a small lawn. When it’s mowed, I don’t rake it. I leave the clippings because they provide aeration and nutrients. When the leaves fall in the autumn, I mulch them and leave them all winter. I also let clover, a nitrogen-fixing plant, grow i my lawn, which stays a nice, healthy green all summer with only a little watering from me when the rains don’t come. As a result, my lawn is thick, velvety and very, very green until the snows fly.
What these over-educated lab rats don’t know about soil, plants, farming and all the rest of it is a lot. If they think that carbon is the only issue, they have rocks in their little pointy heads. They need to spend some time with people who live off the land – the Amish. They use horse-drawn ploughs and harvesting equipment. Those people probably know more about soil conditions than these grant-grubbing people who seldom leave the safety of their labs for the outdoors.
What I find the most peculiar is that they say nothing about comparing soil samples from various parts of a full 640 acre section of farmland, or comparisons between a full section in one place and a full section in another, or samples from farms all over the country, or for successive sampling of the same areas over a period of several years. How many farmers have they interviewed? How many farms have they returned to over a period of 10 years? What sort of factors have they checked against, e.g., rainfall, drought periods, winter snows, fertilizers used – natural or commercial, rough tillage or cleaned up and harvesting volume at the end of the season.? All these things go into good research, not just grabbing a few samples here and there and then making pronouncements.
I take exception to their methods of sampling, testing and reporting, because they aren’t in those areas for full seasonal cycles from spring to spring, nor are they doing repeated testing of the same areas over a prolonged period of time. That kind of work I would be interested in. They come off as just doing a hasty search-snip-and-poke group on the lookout for cash and nothing else.
This narrow focus on one element – carbon – is indicative of poor research methods in addition to a prejudicial bias toward a specific goal, in my opinion. They don’t seem to have a clue how complex the relationship is between plants and dirt. But I guess I’m expecting too much, as always.
Biologists have long known that soil is a large part of the biogeochemical carbon cycle
https://en.wikipedia.org/wiki/Biogeochemical_cycle
The atmosphere is entirely of biological origin (except Argon) which is obvious when considering the geological history of the Earth’s atmosphere, ie atmospheric evolution.
We know that temperatures were much higher in the northern hemisphere after the last ice age (+4-5°C). The tree line was accordingly higher, by 400-500m. As most soil, specifically perma frost, is located in the northern hemisphere, whatever could happen should have happened already.
One nice, strong pine tree (~6.000 years old) released by a melting glacier about 300m above the tree line:
http://oekastatic.orf.at/static/images/site/oeka/20150626/pasterze_baum_michael_avian.5374068.jpg
It must have been an impressive feat, & of significant ceremonial importance, for that specific tree worshiping (druid type) tribal sect to have carted that tree stump all the way up that mountain.
So,DonM, you don’t think it could possibly have grown up there? I’d like to know why you’d think that. There are ancient pine stumps above current treelines in the Swiss-Italian Alps that show those areas were bare of snow some 7,000 years ago and those trees were growing there.
Don just released a little joky feeling; there are people however, who would seriously consider that possibility, to make a stab at skeptics.
Oh, I carried a wooden bench up a mountain once. Yes, some people wondered where it may have come from.
The story only gets “worse”, if you take a closer look. The glacier which released this tree is called “Pasterze”, which does not sound incidentally like pastry. In fact, that is exactly what it means!
Unless ancient people had a strange kind of humor, just like Greenland, the naming here is somewhat humiliating to all those who claim temperatures were never that high in the past. Obviously even only a couple hundred years ago, there was plenty of green, where there still is only ice and snow today.
Soil in “red” states accelerates global warming; soil in “blue” states reduces global warming. See? No conflict.
“They call for a reversal of federal cutbacks to related research programs to learn more about this valuable resource.”
This is the real subject of the article.
Now we are have to make the climate sustainable? Seriously? The rhetoric advances, if not the science.
Sustainable? How about if we ask them to stop breathing our air? You know – wear rebreather equipment or something. Sustainable… oh, the agony of rib-splitting laughter!
Soil science a strong in New Zealand as New Zealand depends on agricultural exports to pay for all the things that other countries can make far cheaper than us .A New Zealand farmer in the South Island holds the world record for wheat tonnage per hectare despite very low natural fertility . Nearly all New Zealand’s soils are phosphate deficient and have had to be top-dressed with super-phosphate for the last 100 years. .Rain or irrigation at the right time with a good depth of friable soil is what is required . Soil mineral deficiencies can be overcome with the right applications .With continuous cropping the organic matter in the soil can drop but under long term pasture organic organic levels rise . This paper sounds very amateurish to me .they are right out of their depth but the one yesterday was plain stoooopid.
Either way soil has got be bad for the Earth’s climate. To avoid all possible effects on climate all soil must be covered with reinforced concrete. In addition use of all goods and services that involve the use of fossil fuels should stop including thouse involved in the making of concrete.
Sequestering CO2 in soils leads to acidification of the soil. Good for growing roses, not good for wheat.
Doesn’t this study also support the premise that warming produces CO2 and not the other way around. Think of all of the peat bogs.
“They buried electrical cables in a set of plots and heated the soil 5° C above the ambient temperature of control plots.” That quote is from yesterday’s article, and I mention it, because the entire experiment was good science; HOWEVER, it does not paint a realistic picture, for soil temperatures to naturally increase that dramatically would require truly catastrophic environmental changes. Outside of the Sun’s blaze engulfing the Earth a few million years from now, there is no decent science to show that transformation occurring.
Sounds like a mixture of Heisenberg uncertainty principle and Schrödinger’s cat. The soil will slow / accelerate warming at the same time.
However, if we keep the soil covered in vegetation and hydrated then it will be kept cool. Open it up to the sun and drain it and it will bake in the sun, warm up the air in contact with it and hey presto it will be hotter. And not hotter in terms of tenths of degrees but whole degrees hotter.
The mind boggles at this weird thinking. It is well reported that cool sea water absorbs CO2 and warm sea water absorbs less. So with both warming land and warming sea CO2 levels are climbing. If CO2 makes things warmer this is known as positive feedback. We are doomed!
Question is why hasn’t it happened before when recorded CO2 levels were much higher than the present?