Climate Explained: What the World Was Like the Last Time Carbon Dioxide Levels Were at 400ppm
By James Shulmeister
Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.
If you have a question you'd like an expert to answer, please send it to [email protected]
What was the climate and sea level like at times in Earth’s history when carbon dioxide in the atmosphere was at 400ppm?
The last time global carbon dioxide levels were consistently at or above 400 parts per million (ppm) was around four million years ago during a geological period known as the Pliocene Era (between 5.3 million and 2.6 million years ago). The world was about 3℃ warmer and sea levels were higher than today.
We know how much carbon dioxide the atmosphere contained in the past by studying ice cores from Greenland and Antarctica. As compacted snow gradually changes to ice, it traps air in bubbles that contain samples of the atmosphere at the time. We can sample ice cores to reconstruct past concentrations of carbon dioxide, but this record only takes us back about a million years.
Beyond a million years, we don't have any direct measurements of the composition of ancient atmospheres, but we can use several methods to estimate past levels of carbon dioxide. One method uses the relationship between plant pores, known as stomata, that regulate gas exchange in and out of the plant. The density of these stomata is related to atmospheric carbon dioxide, and fossil plants are a good indicator of concentrations in the past.
Another technique is to examine sediment cores from the ocean floor. The sediments build up year after year as the bodies and shells of dead plankton and other organisms rain down on the seafloor. We can use isotopes (chemically identical atoms that differ only in atomic weight) of boron taken from the shells of the dead plankton to reconstruct changes in the acidity of seawater. From this we can work out the level of carbon dioxide in the ocean.
The data from four-million-year-old sediments suggest that carbon dioxide was at 400ppm back then.
Sea Levels and Changes in Antarctica
During colder periods in Earth's history, ice caps and glaciers grow and sea levels drop. In the recent geological past, during the most recent ice age about 20,000 years ago, sea levels were at least 120 meters lower than they are today.
Sea-level changes are calculated from changes in isotopes of oxygen in the shells of marine organisms. For the Pliocene Era, research shows the sea-level change between cooler and warmer periods was around 30-40 meters and sea level was higher than today. Also during the Pliocene, we know the West Antarctic Ice Sheet was significantly smaller and global average temperatures were about 3℃ warmer than today. Summer temperatures in high northern latitudes were up to 14℃ warmer.
This may seem like a lot but modern observations show strong polar amplification of warming: a 1℃ increase at the equator may raise temperatures at the poles by 6-7℃. It is one of the reasons why Arctic sea ice is disappearing.
Impacts in New Zealand and Australia
In the Australian region, there was no Great Barrier Reef, but there may have been smaller reefs along the northeast coast of Australia. For New Zealand, the partial melting of the West Antarctic Ice Sheet is probably the most critical point.
One of the key features of New Zealand's current climate is that Antarctica is cut off from global circulation during the winter because of the big temperature contrast between Antarctica and the Southern Ocean. When it comes back into circulation in springtime, New Zealand gets strong storms. Stormier winters and significantly warmer summers were likely in the mid-Pliocene because of a weaker polar vortex and a warmer Antarctica.
It will take more than a few years or decades of carbon dioxide concentrations at 400ppm to trigger a significant shrinking of the West Antarctic Ice Sheet. But recent studies show that West Antarctica is already melting.
Sea-level rise from a partial melting of West Antarctica could easily exceed a meter or more by 2100. In fact, if the whole of the West Antarctic melted it could raise sea levels by about 3.5 meters. Even smaller increases raise the risk of flooding in low-lying cities including Auckland, Christchurch and Wellington.
James Shulmeister is a professor at the University of Canterbury.
Disclosure statement: James Shulmeister receives funding from the Australian Research Council and is part of a National Science Foundation grant from the US. As well as being Professor and Head of School at the University of Canterbury in New Zealand, he is an Adjunct Professor at the University of Queensland, Australia and an associate investigator at the ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH).
Reposted with permission from The Conversation.
- Scientists Sound the Alarm: CO2 Levels Race Past Point of No Return ›
- Global Carbon Levels Surpass 400 ppm for First Time Ever for Entire ... ›
- Carbon Dioxide Levels Set to Pass 400 ppm and Remain Above ... ›
- Two Canadian Ice Caps Disappear Completely - EcoWatch ›
By Brett Wilkins
While some mainstream environmental organizations welcomed Tuesday's introduction of the CLEAN Future Act in the House of Representatives, progressive green groups warned that the bill falls far short of what's needed to meaningfully tackle the climate crisis—an existential threat they say calls for bolder action like the Green New Deal.
<div id="25965" class="rm-shortcode" data-rm-shortcode-id="6116a1c2b1b913ad51c3ea576f2e196c"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1366827205427425289" data-partner="rebelmouse"><div style="margin:1em 0">BREAKING: Rep @FrankPallone just released his CLEAN Future Act — which he claims to be an ambitious bill to combat… https://t.co/M7nR0es196</div> — Friends of the Earth (Action) (@Friends of the Earth (Action))<a href="https://twitter.com/foe_us/statuses/1366827205427425289">1614711974.0</a></blockquote></div>
<div id="189f0" class="rm-shortcode" data-rm-shortcode-id="aa31bacec80d88b49730e8591de5d26d"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1366863402912657416" data-partner="rebelmouse"><div style="margin:1em 0">The CLEAN Future Act "fails to grasp the fundamental truth of fighting climate change: We must stop extracting and… https://t.co/yREn6Qx9tn</div> — Food & Water Watch (@Food & Water Watch)<a href="https://twitter.com/foodandwater/statuses/1366863402912657416">1614720605.0</a></blockquote></div>
- Biden Plans to Fight Climate Change in a New Way - EcoWatch ›
- Bipartisan Climate Bill Highlights Forest Restoration, Conservation ... ›
EcoWatch Daily Newsletter
- Redwoods are the world's tallest trees.
- Now scientists have discovered they are even bigger than we thought.
- Using laser technology they map the 80-meter giants.
- Trees are a key plank in the fight against climate change.
They are among the largest trees in the world, descendants of forests where dinosaurs roamed.
Pixabay / Simi Luft<p><span>Until recently, measuring these trees meant scaling their 80 meter high trunks with a tape measure. Now, a team of scientists from University College London and the University of Maryland uses advanced laser scanning, to create 3D maps and calculate the total mass.</span></p><p>The results are striking: suggesting the trees <a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank" rel="noopener noreferrer">may be as much as 30% larger than earlier measurements suggested.</a> Part of that could be due to the additional trunks the Redwoods can grow as they age, <a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank" rel="noopener noreferrer">a process known as reiteration</a>.</p>
New 3D measurements of large redwood trees for biomass and structure. Nature / UCL<p>Measuring the trees more accurately is important because carbon capture will probably play a key role in the battle against climate change. Forest <a href="https://www.wri.org/blog/2020/09/carbon-sequestration-natural-forest-regrowth" target="_blank">growth could absorb billions of tons</a> of carbon dioxide from the atmosphere each year.</p><p>"The importance of big trees is widely-recognised in terms of carbon storage, demographics and impact on their surrounding ecosystems," the authors wrote<a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank"> in the journal Nature</a>. "Unfortunately the importance of big trees is in direct proportion to the difficulty of measuring them."</p><p>Redwoods are so long lived because of their ability to <a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank" rel="noopener noreferrer">cope with climate change, resist disease and even survive fire damage</a>, the scientists say. Almost a fifth of their volume may be bark, which helps protect them.</p>
Carbon Capture Champions<p><span>Earlier research by scientists at Humboldt University and the University of Washington found that </span><a href="https://www.sciencedirect.com/science/article/pii/S0378112716302584" target="_blank" rel="noopener noreferrer">Redwood forests store almost 2,600 tonnes of carbon per hectare</a><span>, their bark alone containing more carbon than any other neighboring species.</span></p><p>While the importance of trees in fighting climate change is widely accepted, not all species enjoy the same protection as California's coastal Redwoods. In 2019 the world lost the equivalent of <a href="https://www.worldwildlife.org/threats/deforestation-and-forest-degradation" target="_blank" rel="noopener noreferrer">30 soccer fields of forest cover every minute</a>, due to agricultural expansion, logging and fires, according to The Worldwide Fund for Nature (WWF).</p>
Pixabay<p>Although <a href="https://c402277.ssl.cf1.rackcdn.com/publications/1420/files/original/Deforestation_fronts_-_drivers_and_responses_in_a_changing_world_-_full_report_%281%29.pdf?1610810475" target="_blank" rel="noopener noreferrer">the rate of loss is reported to have slowed in recent years</a>, reforesting the world to help stem climate change is a massive task.</p><p><span>That's why the World Economic Forum launched the Trillion Trees Challenge (</span><a href="https://www.1t.org/" target="_blank" rel="noopener noreferrer">1t.org</a><span>) and is engaging organizations and individuals across the globe through its </span><a href="https://uplink.weforum.org/uplink/s/uplink-issue/a002o00000vOf09AAC/trillion-trees" target="_blank" rel="noopener noreferrer">Uplink innovation crowdsourcing platform</a><span> to support the project.</span></p><p>That's backed up by research led by ETH Zurich/Crowther Lab showing there's potential to restore tree coverage across 2.2 billion acres of degraded land.</p><p>"Forests are critical to the health of the planet," according to <a href="https://www.1t.org/" target="_blank" rel="noopener noreferrer">1t.org</a>. "They sequester carbon, regulate global temperatures and freshwater flows, recharge groundwater, anchor fertile soil and act as flood barriers."</p><p><em data-redactor-tag="em" data-verified="redactor">Reposted with permission from the </em><span><em data-redactor-tag="em" data-verified="redactor"><a href="https://www.weforum.org/agenda/2021/03/redwoods-store-more-co2-and-are-more-enormous-than-we-thought/" target="_blank">World Economic Forum</a>.</em></span></p>
- Offshore Wind Power Is Ready to Boom. Here's What That Means for ... ›
- American Skyscrapers Kill an Estimated 600 Million Migratory Birds ... ›
Kentucky is coping with historic flooding after a weekend of record-breaking rainfall, enduring water rescues, evacuations and emergency declarations.
<div id="0f31c" class="rm-shortcode" data-rm-shortcode-id="4290ab3e7ec4e142f8bce774bab39f03"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1366307788155219969" data-partner="rebelmouse"><div style="margin:1em 0">Just got back from my office... downtown Beattyville Kentucky is not a pretty sight. @KySportsRadio… https://t.co/6nXwyMKtRb</div> — Tom Jones (@Tom Jones)<a href="https://twitter.com/8atticus/statuses/1366307788155219969">1614588136.0</a></blockquote></div>
<div class="rm-shortcode" data-rm-shortcode-id="b41a2da6bf23cc19a5f38c2dc6c5f9fc"><div class="fb-post" data-href="https://www.facebook.com/dekalbtnfire/photos/a.924258171004562/3713119618785056/"></div></div>
Spring is coming. And soon, tree swallows will start building nests. But as the climate changes, the birds are nesting earlier in the spring.
- Spring Is Arriving Earlier Across the U.S. - EcoWatch ›
- Climate Change Leading to Fatal Bird Conflicts - EcoWatch ›
- The Unsettling Reason Why We're Seeing More Snowy Owls ... ›