The leader of the South Pacific island nation of Kiribati laid out an extraordinary plan Monday (Sept. 22) that would scatter his people through the nations of the world as rising sea levels submerge the islands they have called home for centuries.

Rising sea levels are submerging the land. Land not yet submerged is being rendered uninhabitable by salty ground water.

This post is by Sheryl Canter, an online writer and editorial manager at Environmental Defense Fund.

One reason for the acceleration in CO₂ concentrations is higher fossil fuel emissions. Despite rising fuel prices, global CO₂ emissions from fossil fuels rose 3 percent in 2007. That's just slightly below the average increase of 3.5 percent per year since 2000.

The rate of increase for emissions lies at the upper end of the range projected by the IPCC, suggesting that we're headed towards the most disruptive scenarios they envision. Action to stop climate change is urgent.

Check out the full report for details on what factors account for the increase. Also, the Dot Earth and Climate Progress blogs have interesting takes on the report.

This post is by James Wang, Ph.D., a climate scientist at Environmental Defense Fund.

At Mohonk, the weather observations are done as they were 112 years ago, and only a handful of people have recorded the over 41,000 readings. Plus Mohonk has an extensive database of wildlife sightings, a 77-year record of Mohonk Lake water quality, and an 83-year record of local phenology (the timing of events such as frost, blooms and migrations) – all observed by the same handful of people. This makes the site's data uniquely valuable:

• Mohonk House's records were used in Environmental Defense Fund's successful effort to reduce acid rain.
• In the 1950s, Mohonk House stopped using the pesticide DDT, because careful daily observations suggested it was killing local wildlife. (Winning a national ban on DDT was Environmental Defense Fund's first campaign.)
• The phenological data lets researchers track the effects of climate change on various species. (For more, see Bill's post on shifts in lifecycle timing.)

Local phenology records are extremely valuable, and can be fun to collect and explore. Project Budburst is a network of "citizen scientists" observing phenological events. Do you participate, or would you like to? Share your thoughts and stories here!

This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense Fund.

Have you ever spent time scrolling through NASA's image gallery? Some of the pictures are mesmerizing. I particularly like the "Blue Marble" image of the Earth (at right), which was stitched together using satellite data.

Satellites provide more than pretty pictures. Our ability to understand and predict climate change depends on continuous high-quality satellite data.

Unfortunately, this critical data stream is threatened by budget cuts and lack of political support. In 2005, the National Academies assessed the situation and deemed it "alarming". Three years later, the outlook has not improved.

What Satellites Can Tell Us

Here are just a few examples of the indispensible role satellites play in weather and climate science. Satellites have provided a way to:

• Confirm that global warming is not caused by changes in the Earth's reflectivity or "albedo".
• Monitor and verify changes in deforestation emissions (key to any plan to reduce deforestation in developing countries).
• Track ice sheet melting and sea level rise.
• Predict and track storms and floods.
• Improve accuracy of climate models in simulating atmospheric temperature trends, the effects of aerosol pollution, and more.

But crucial information like this may not be available in the future. Many planned satellite missions have been delayed, pared down, or cancelled due to budget cuts. For example, sensors that would have measured important climate-related variables such as solar irradiance, aerosols, and sea level have been removed from the upcoming National Polar-orbiting Operational Environmental Satellite System.

Existing satellites don't last forever, so these cutbacks put long-term records at risk, precisely when we need all the information we can get about climate change and its effects.

We Need Funding for Satellites

The National Academies Press has published several reports (here, here, and here) proposing short-term solutions that would avoid gaps in crucial datasets. But what we really need is a long-term commitment to a unified, high-quality Earth observation program.

This issue is so pressing that it was highlighted in a recent editorial in the journal Nature, which called on the next U.S. president to make Earth observation a priority. As Nature put it, "Providing for continuous high-quality climate data would be a substantial legacy, serving the interests of both U.S. citizens and the rest of the world for decades to come."

In 1992, the world's nations gathered to negotiate the United Nations Framework Convention on Climate Change. The 192 nations that ratified this treaty – including the U.S. – agreed to the following objective:

[T]o … prevent dangerous anthropogenic interference with the climate system… within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner.

The definition of "dangerous" is a social and political judgment that is informed by science. But even if we all agreed on which outcomes we wanted to avoid, scientists couldn't say precisely how much we have to cut emissions to achieve these outcomes. We have good best estimates, but there's always a degree of scientific uncertainty.

Here's why.

There are essentially three layers of uncertainty in quantifying the impacts of climate change:

• How emissions affect greenhouse gas levels
• How greenhouse gas levels affect climate
• How climate change affects Earth's systems

How emissions affect greenhouse gas levels

Even if we knew exactly what emissions would be in the future, there still would be uncertainty about future greenhouse gas levels.

Plants and the oceans currently act as "carbon sinks", offsetting some of our CO₂ emissions. But we don't fully understand how they will respond as emissions climb. As I wrote in a previous post, it appears that oceans are taking up a smaller fraction of our CO₂ emissions than they did a few decades ago, and we're not sure why.

We also don't know how much CO₂ and methane will be emitted from melting permafrost. Climate feedbacks such as this can greatly accelerate warming.

For these reasons and more, scientists can estimate how greenhouse gas levels will change for a given emissions scenario, but there is uncertainty around that estimate.

How greenhouse gas levels affect climate

Even if we knew exactly what greenhouse gas levels would be in the future, there still would be uncertainty about how climate would change as a result. This is true at the global level, and even more so at the regional level.

Climate feedback processes affect how much climate changes in response to greenhouse gas levels. The degree of impact on climate, called climate sensitivity, is usually quantified as the amount of warming from a doubling of CO₂ levels. Climate sensitivity is estimated with a measure of uncertainty because climate feedback processes that affect it cannot be precisely measured.

The latest IPCC report (WG1, Chapter 10) estimates that global climate sensitivity is "most likely" 3.0°C (5.4°F), with a "likely range" of 2 to 4.5°C (about 3.6 to 8°F). But the report goes on to say that somewhat lower or "substantially higher" values cannot be ruled out.

On the regional scale, there is even more uncertainty.

How climate change affects Earth's systems

In my post on tipping elements, I described nine Earth systems that are especially vulnerable to climate change – for example, Arctic summer sea ice and the Greenland ice sheet. If Earth systems like these are pushed past their tipping points, the resulting changes would have catastrophic effects on ecosystems and people. The latest IPCC report (WG2) devotes an entire chapter to this issue (Chapter 19, "Assessing key vulnerabilities and the risk from climate change").

But even if we knew exactly how much temperatures were going to rise, we could not say with certainty what the impact would be on Earth's systems. We don't know the precise temperature that will trigger severe or irreversible changes. Scientists' best estimates, like those for greenhouse gas levels and temperatures, come in ranges.

For example, various studies estimate that Greenland could begin an irreversible meltdown once global average temperature rises 2.2 to 7.0°F above today's temperature. With the warming in the pipeline, we're just 1.2°F away from the lower end of that danger zone.

That's already too close for comfort, but it may be even worse; scientists may have overestimated the resilience of ice sheets and other tipping elements to increasing temperature. Arctic summer sea ice is melting faster than predicted. Maybe this rapid loss is natural, random, and temporary, or maybe we're closer to a tipping point than scientists thought. We don't know for sure.

Adding up the uncertainties

The estimates of what we care about most – the impact on Earth's systems – are based upon factors that are themselves estimates and subject to uncertainty. These uncertainties combine, so we end up with a best estimate surrounded by a wide range of uncertainty.

That's why, even if nations could agree on which dangerous changes they want to avoid, scientists could not pinpoint the precise emissions levels that would guarantee that outcome.

Still, there are some things we know for sure. Scientists have no doubt that human-induced global warming is happening, and that the consequences, unchecked, are very dangerous. The uncertainty is only around exactly when and how it will play out.

IPCC scientists have been saying for years that man-made global warming is likely to increase extreme weather events. A new report ("Weather and Climate Extremes in a Changing Climate") from U.S. government scientists confirms these findings, and focuses specifically on the U.S.

It's certainly timely, considering the devastating floods in the Midwest.

The report describes how U.S. weather is becoming more extreme, and links much of this change to human-induced global warming:

• "[M]ost of North America has been experiencing more unusually hot days and nights"
• "Heavy downpours have become more frequent and intense"
• "Droughts are becoming more severe in some regions"

And what do they say about the future? According to model projections under a business-as-usual scenario:

• "A day so hot that it is currently experienced once every 20 years would occur every other year or more by the end of the century."
• Extreme downpours "that occur on average every 20 years in the present climate would, for example, occur once every 4-6 years for Northeast North America."
• "[W]ith continued global warming, heat waves and heavy downpours are very likely to further increase in frequency and intensity. Substantial areas of North America are likely to have more frequent droughts of greater severity. Hurricane wind speeds, rainfall intensity, and storm surge levels are likely to increase. The strongest cold season storms are likely to become more frequent, with stronger winds and more extreme wave heights."

The record floodwaters in Iowa and other parts of the Midwest are claiming lives, destroying homes and crops, contaminating drinking water, and – as the AP puts it – spreading "a noxious brew of sewage, farm chemicals, and fuel that could sicken anyone who wades in." The cost in human anguish is incalculable.

But why is it happening? Is it just a freak of nature? One causal element, as reported in today's Washington Post, may be human reengineering of the landscape. Mary Kelly, who heads up EDF's rivers and deltas program, gives a good overview of these issues.

Another element may be global warming, which increases the probability of extreme weather events like torrential rain.

Global Warming and Heavy Rainfall

Global warming intensifies the "hydrological cycle" – the process in which water evaporates into the air, forms clouds, and then rains back down on the Earth.

Higher temperatures cause evaporation to occur more quickly. This can cause very dry conditions on land, even drought. But there's another side to it. The greater amount of water vapor that a warm atmosphere can hold causes wetter clouds to form, so the rain, when it comes, can be unusually heavy – heavy enough to cause flooding. This intensification of the hydrological cycle causes some seasons to be very wet while others are very dry.

We can't say for sure that global warming caused the unusually heavy rain in the Midwest – or any specific weather event. But we can say that the probability of torrential rainfall is increased due to global warming.

The IPCC's 2007 report [PDF] says:

• "The frequency of heavy precipitation events has increased over most land areas, consistent with warming and observed increases of atmospheric water vapour."
• "It is very likely that hot extremes, heat waves and heavy precipitation events will continue to become more frequent."

Global warming doesn't fully explain the catastrophe in the Midwest, but it likely plays a role. The sooner we can bring emissions under control, the better.

In IPCC's Third Assessment Report (2001), scientists reported that carbon dioxide (CO₂) and methane levels were higher than at any time in the past 420,000 years. In their latest report (2007), IPCC scientists raised the number to 650,000 years.

Last week, scientists again revised the number upward. New research shows that CO₂ and methane levels are higher today than they have been in at least 800,000 years.

Here's how they know.

The research, published in Nature, analyzes the atmospheric gases trapped in ice cores extracted from Antarctica. These ice cores are the oldest yet studied. In 2001, the 420,000-year old Vostok ice core from eastern Antarctica set the benchmark. In 2005, scientists analyzed a 650,000-year record from Antarctica's Dome C. Now, drilling even deeper, scientists at Dome C have assembled an 800,000 year record of CO₂, methane and temperature.

These are the main findings:

• CO₂ and methane levels are higher today than they have been in at least the past 800,000 years.
• The strong correlations of methane and CO₂ with temperature reconstructions are consistent back 800,000 years.
• The long-term cyclic changes in temperature, methane and CO₂ that follow slow changes in Earth's orbit are consistent back 800,000 years.

CO₂ (red) is in parts-per-million (ppm); methane (green) is in parts-per-billion (ppb); temperature (black) is relative to the average of the past millennium.  Reprinted by permission from Macmillan Publishers Ltd: Nature. "Windows on the greenhouse" by Ed Brook, Nature 453: 291-292, copyright 2008.

There are no surprises in the big picture, but more detailed analysis raises some intriguing questions. For example:

• Cold phases remain roughly similar throughout the 800,000 year record, but starting about 450,000 years ago, warm phases got warmer. Why?
• What accounts for the unusually low value for CO₂ (172 ppm) about 667,000 years ago?

Scientists are already forming hypotheses about these and other questions. To help find answers, scientists have launched a new project to obtain a 1.5 million year record. That will mean drilling in locations with older ice because they've nearly reached bedrock at Dome C.

In the meantime, one thing is clear: Human activity has had an enormous effect on Earth's natural cycle. It's time to take responsibility for the damage we've caused and cap emissions.

An article in this week's Nature predicts that Europe and North America will cool slightly over the next decade. No, this doesn't mean that global warming has stopped.

The new paper describes a climate model that makes short-term (decadal) predictions based on ocean dynamics. The decade-long cooling is just a temporary offset to warming from human activity. After it passes, temperatures will begin climbing again. By 2030, the model forecasts the same global temperatures as the IPCC.

Last week, NOAA released some disheartening numbers: both CO₂ and methane increased sharply last year. Growth rates are increasing (see graph to the right).

The CO₂ numbers weren't a surprise. A paper with similar findings was published last November by a team that included a NOAA scientist. I wrote a blog post summarizing the study, which analyzed the reasons behind the trend (see Rise of Atmospheric Carbon is Accelerating).

The methane numbers, however, were disturbing. Until this year, methane levels have been essentially unchanged since 1998.

Scientists worry that melting permafrost could release large amounts of methane, setting off a dangerous feedback process. Fortunately, last year's methane increase doesn't appear to come from permafrost, though researchers are continuing to watch for signs.

The rise in methane, scientists think, is most likely from "rapidly growing industrialization in Asia and rising wetland emissions in the Arctic and tropics."

These accelerating increases in greenhouse gas pollution are a reminder that we can't be complacent about global warming. Also, non-CO₂ emissions can't be ignored. We must reduce all the emissions we can control, and turn these trends around. It's time to cap emissions!