What does 'net zero' mean? Our climate change glossary will help you sound smart

(CNN)The whole world seems to be talking about the climate crisis, thanks to months of wild weather and new science showing that we need to act quicker than we previously thought to avoid the worst consequences.

As leaders prepare to meet in Glasgow, Scotland, next month for crunch talks, they'll be using a lot of technical lingo. The terminology isn't particularly communicative and can be daunting.
Even the name of the summit -- COP26 -- sounds more like a bad police drama than a climate event. (First pointer: COP is short for Conference of the Parties to the UN Convention on Climate Change. It convenes global leaders, scientists and negotiators on climate, and usually takes place annually. The "26" means Glasgow will be the 26th meeting.)
    Here are other terms to know to keep up with the talks, understand what's at stake and, most importantly, sound smart around the dinner table.

      Net zero emissions

      Net zero emissions can be achieved by removing as much greenhouse gas from the atmosphere as what's emitted, so the net amount added is zero. To do this, countries and companies will need to rely on natural methods -- like planting trees or restoring grasslands -- to soak up carbon dioxide (CO2), the most abundant greenhouse gas we emit, or use technology to "capture" the gas and store it away where it won't escape into the atmosphere.
      Dozens of countries have already pledged to achieve net zero by mid-century and there is huge pressure on countries that haven't yet to do so by COP26.

      Negative emissions

      To save the world from the worst effects of climate change, scientists say it's probably not enough to reach net zero. Net negative emissions is the situation where the amount of greenhouse gas removed from the atmosphere is actually more than the amount humans emit at a given period of time.

      Carbon sinks

      A container of young silver firs at a forest tree nursery in Pockau-Lengefeld, Germany.
      This is a reservoir that absorbs carbon dioxide from the atmosphere and locks it away.
      Natural sinks like trees and other vegetation remove CO2 from the atmosphere through photosynthesis -- plants use the carbon dioxide in the atmosphere to grow. The ocean is also a major carbon sink because of phytoplankton which, as a plant, also absorbs carbon dioxide.
      Scientists say preservation and expansion of natural sinks such as forests are crucial to reducing emissions.
      There are also artificial carbon sinks that can store carbon and keep it out of the atmosphere. More on that below.

      Carbon capture and storage

      Technology to remove and contain carbon dioxide from the atmosphere is known as carbon capture and storage. Carbon is usually captured at source -- directly from coal, oil or gas as it burns -- but new technology is being developed to literally suck carbon from the air.
      In both cases, the carbon can be stored, usually buried in reservoirs underground or below the floor of the sea, in what are known as artificial carbon sinks. Some scientists warn that it could be risky to inject so much carbon underground, and this process isn't currently used on a large scale. The Global CCS Institute says just 27 commercial facilities are fully operating worldwide, while more than 100 others are in development. But other experts say CCS is necessary to put a real dent in our emissions.
      There are many ways to capture and store carbon. Here are some of them:
      • Carbon dioxide capture and storage (CCS) is a process in which CO2 produced by heavy industry or power plants is collected directly at the point of emission, compressed and transported for storage in deep geological formations.
      • Carbon capture, utilization and storage (CCUS) refers to the collection of CO2 from industrial sources, which is then used to create products or services, such as manufacturing fertilizer or in the food and beverage industry. (Fun fact: This CO2 can be pumped into your beer to make it fizzy.)
      • Direct air capture and storage (DACS, DAC or DACC) is a chemical process which removes CO2 directly from the air for storage. There were 15 direct air capture plants operating worldwide, according to a June 2020 International Energy Agency (IEA) report.


      Nationally Determined Contributions -- or NDCs -- is a term used by the UN for each country's individual national plan to slash greenhouse gas emissions.
      In the 2015 Paris Agreement, which nearly the whole world signed on to, countries were given the freedom to determine themselves how they would go about meeting the agreement's key targets to slow global warming.
      NDCs are supposed to be updated every five years and submitted to the UN, the idea being that each country's ambition will grow over time. Dozens of countries have failed to submit their updates ahead of COP26.

      Pre-industrial levels

      Smokestacks at Skoda's main foundry in Pilsen, then part of  Czechoslovakia, on August 29, 1938.
      This usually refers to average concentration of carbon dioxide in the atmosphere before the Industrial Revolution, which started in the late 18th century. CO2 levels are estimated to have been around 280 parts per million at that time. By 2020, that concentration had risen to 412.5 parts per million, according to US government figures.
      Scientists also talk about pre-industrial levels for average temperatures, using the period 1850-1900 to determine how hot or cold the Earth was before humans began emitting greenhouse gases at larger volumes, like those we see today.

      1.5 degrees

      A key goal of COP26 President Alok Sharma, a British MP, is "keeping 1.5 alive," which refers to a target to keep average global temperature rise to 1.5 degrees Celsius above pre-industrial levels. It's a target that some fossil fuel-producing countries have resisted, and scientists have warned of significantly worse impacts if this threshold is breached.
      The countries that signed the Paris Agreement in 2015 agreed to limit the increase in global temperatures to well below 2 degrees above pre-industrial levels, but preferably to 1.5 degrees. However, an analysis released last month by watchdog Climate Action Tracker (CAT) found that not a single major economy -- including the entire G20 -- had a climate plan that meets its obligations under Paris.
      The United Nations' Intergovernmental Panel on Climate Change (IPCC) said in its latest state-of-the-science report that the world has already warmed by 1.1 degrees above than pre-industrial levels, and is now hurtling fast toward 1.5 degrees.

      Climate finance

      More than 10 years ago, at COP16 in Cancún, Mexico, the developed world agreed to transfer money to developing countries to help them limit or reduce their greenhouse gas emissions and adapt to the climate crisis. They set up the Green Climate Fund (GCF) to facilitate some of this transfer, but countries and donors can send money through any means they like.
      The money was supposed to build up and reach $100 billion annually by 2020, and that commitment was reaffirmed in the Paris Agreement. This money is often referred to broadly as "climate finance."
      But the 2020 target was missed, and filling the gap is high on the agenda for the talks in Glasgow.
      Developing nations, particularly those in the Global South, which are most vulnerable to the effects of climate change, argue that industrialized nations are historically more responsible for climate change and must do more to fund changes to help developing nations adapt.
      US President Joe Biden pledged to double the US' existing contribution plans, including money for the Green Climate Fund, in a speech at the UN General Assembly in September. Some critics say he should pledge more to make up for the Trump years, when no money was paid into the fund.