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Climate Change in China

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Climate Change in China and Risks

Climate Background in China

From observed, historical data, China’s climate context for current climatology, 1991-2020. In order to appreciate future climate scenarios and projected change, information should be used to develop a strong understanding of current climate conditions. Data for the current climatology can be visualized using spatial variation, the seasonal cycle, or a time series. Both annual and seasonal data can be analyzed. The data presentation defaults to national-scale aggregation; however, sub-national data aggregations can be accessed by clicking on a sub-national unit within a country.

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Observed, historical data is produced by the University of East Anglia’s Climatic Research Unit (CRU). The data is presented at a resolution of 0.5o x 0.5o (50km x 50km).

Climate Change in China

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Climate trends, past, present, and future, must always be understood in the context of naturally occurring variability. Climate variability here, refers to the ways how climate conditions (e.g., temperature and precipitation) “flicker” from year to year within their respective typical “range of variability”. The cause of this natural variability could be due to the coupled atmosphere-ocean-land-ice system’s quasi-random internal variability (as weather variability is drawn out over many years). El Nio-Southern Oscillation variability is a prime example of a cause in this category.

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Other causes include the influence of non-human nature’s periodic “forcing” events, such as explosive volcanic eruptions. These natural factors (internal as well as natural forcing) are summarized under “internal climate variability”. This internal climate variability is always present, sometimes more pronounced, sometimes less so. As a result, climatology must be understood as a mean with variability around it. Variability can be very high from year to year (high latitudes), or it can be very low in a few locations and for specific variables (i.e., temperatures in the tropics).

In contrast to natural variability, anthropogenic greenhouse gas emissions and changes in atmospheric concentrations (i.e., CO2, methane) combined with land surface changes and aerosol impose a different forcing on the climate system. The search for climate change signals attempts to distinguish their effects from natural background variability. This signal can manifest itself as changes in the magnitude of the variability as well as a systematic trend over time.

Climate Change in China
Climate Change in China

This page provides three themes for exploring and comprehending differences in variability, trends, and the significance of change over the last 70, 50, and 30 years. It is intended to supplement the views on the climatology pages with information (Current Climatology- Climatology tab). The three sections present various aspects of how variability may need to be considered. The variables presented are only a subset of the full indicator catalog for ease of navigation. The data on this page is derived from the ERA5 reanalysis (at 0.5o x 0.5o resolution) in order to extract daily variability.

Climate Change Risks in China

A high-level understanding of extreme events and how they differ from average climate. Extremes are frequently associated with physical processes that are distinct from those that govern long-term means. While average precipitation changes are primarily caused by changes in circulation, extremes are much more sensitive to the thermodynamic state and conditions on specific days. As a result, it is critical to compare and contrast trends and projections in means with those of rare events.

Extremes can occur only when several preconditions are met. Extreme rainfall, for example, necessitates maximum (“potential”) moisture transport into the region, high temperatures (or large temperature gradients), and significant atmospheric instability. An alignment of these “ingredients” is uncommon. Some of these conditions, however, may see a systematic increase in occurrence as a result of climate change, which is especially true for global temperatures. If that one condition – higher temperatures – is met more frequently, the likelihood of a combined occurrence increases.

Warmer temperatures are especially important for precipitation because the Clausius-Clapeyron-Relationship states that each 1oC increase in air temperature increases the air’s ability to carry moisture by 7%. Thus, the warmer the air, the more moisture it “can” carry, and thus, if rain falls, much more water can be tapped into.

Where the most extreme precipitation may occur is also uncertain, as current local conditions over a larger region can dictate the dynamical process of triggering an event, though physical settings (e.g., topography) can sometimes lead to areas with a higher likelihood of occurrence. Overall, extreme events must be viewed as requiring a set of prerequisites coupled with a probabilistic element of initiation. This is why severe thunderstorms can affect one location while barely any precipitation is recorded a few kilometers away.

When compared to mean precipitation, extreme precipitation events may exhibit different signs and, in most cases, larger magnitudes of change. (2) As the world warms, the ability of air to carry moisture increases exponentially, increasing the possibility of heavier precipitation. This means that intense events will likely occur more frequently, potentially increasing the risk of flooding. Only in areas where precipitation occurrence decreases significantly can the trend toward heavier rainfall be reversed, and return periods of large events increase rather than decrease.

The baseline climate (from 1985 to 2014, centered on 2000) can be compared to future time periods and scenarios, centered on 2025, 2050, 2075, and 2085. (using data to the end of the century). Please keep in mind that the presented extreme indicators are qualitative projections that directly reflect global model output and should not be confused with location-specific (“station-level”) extremes.

Climate Change and Coastal Risks

The planet’s systematic warming is directly causing global mean sea level to rise in two ways: (1) melting mountain glaciers and polar ice sheets add water to the ocean, and (2) warming of the water in the oceans leads to expansion and thus increased volume. Since 1880, global mean sea level has risen by about 210-240 millimeters (mm), with nearly a third occurring in the last two and a half decades. The annual rise is currently around 3mm per year. Regional variations exist as a result of natural variability in regional winds and ocean currents, which can last for days, months, or even decades.

However, other factors such as ground uplift (e.g., continued rebound from Ice Age glacier weight) or subsidence, changes in water tables due to water extraction or other water management, and even the effects of local erosion can all play a role locally.

Rising sea levels put a strain on not only the physical coastline, but also on coastal ecosystems. Saltwater intrusions have the potential to contaminate freshwater aquifers, which support municipal and agricultural water supplies as well as natural ecosystems. Because there is a significant lag in reaching an equilibrium, sea level will continue to rise as global temperatures continue to rise. The magnitude of the rise will be heavily influenced by future carbon dioxide emissions and global warming, and the rate of rise may become increasingly influenced by glacier and ice sheet melting.

 

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