Grapevine phenology has two developmental cycles known as the vegetative and reproductive cycles. These cycles are complex and include vine and fruit growth for the current season as well as the next. These cycles are responsible for berry formation and growth of the vine. There is a strong correlation between grapevine phenology and environmental factors, such as daylight length, heat, water, soil, and light. Climate change factors, such as elevated CO₂, elevated temperatures, and water stress, have played an important role in grapevine growth patterns ^[1][22].

Carbon dioxide is a major concern with climate change as the atmospheric CO₂ concentration is expected to reach 600 ppm. High CO₂ levels may promote physiological changes in vines. Increasing CO₂ levels will limit the production of plant hormones, such as ethylene and jasmonic acid, which are both significant in the plants’ defense response ^[2][23].

Temperatures can affect grape quality by leading to an earlier onset of the growing season, creating premature véraison from early heat, which can affect enzyme activation or cause poor ripening. This would cause the growing season to be shortened and accelerate berry ripening ^[3][24]. When the sugar accumulation starts earlier and progresses more rapidly in the warmer periods of the growing season, the phenolic composition and berry anthocyanin concentration can be negatively affected, causing less than desirable harvest levels. For example, during flowering and the berry growth period, heat extremes can cause berry softening and changes in berry color. It has been shown that the accumulation of anthocyanins, which are responsible for berry coloration, is lower when maturation occurs at higher temperatures ^[4][25]. Premature véraison might lead to less aroma and flavor compound accumulation, which can affect berry flavor development ^[5][26]. Similar observations have been made in different wine regions ^[6][7][8][9][27,28,29,30]. In summary, increasingly high temperatures would lead to negative outcomes for grape and wine quality.

A major factor affecting the growth and productivity of the vine is water availability. Climate change is associated with unpredictable precipitation patterns and more severe drought conditions that can be expected to impact yield and the overall growth of vines. When water shortages occur early in the season, they can reduce yield by affecting bud fertility, as the reproductive structures inside the dormant buds are sensitive during this time ^[10][31]. Once the grapevine gets past budbreak, the reproductive growth is relatively unaffected. Another effect of climate change is the combination of higher temperatures and unpredictable precipitation, leading to water deficits. High rates of evapotranspiration and increased plant water requirements are caused by higher temperatures ^[11][32]. When water deficits are up to 50% of the evapotranspiration threshold, there is almost no effect on yield; however, when the threshold is surpassed, the yield decreases. This phenomenon is more prominent during the budbreak to bloom phenological phase ^[12][13][33,34].

Studies have found that climate change is inducing greater pest and disease pressure in vineyards. A healthy vine can create resistance or fight off potential attacks due to the plant’s defense system. Pests or pathogens usually affect the vine during specific exposed periods of the vine’s lifecycle. However, climate change can modify the period a plant will be exposed to a pathogen. For instance, high temperatures would promote pathogen development and increase survival rates, which can change the susceptibility of a host (plant) to pests and diseases ^[14][35].

Plant diseases can be used as an indicator of climate change. This can be complicated with all the biological interactions that result in disease ^[14][35]. Disease will occur more often when the vines are stressed in warmer climates. There is a concern regarding diseases that increased CO₂ levels will decrease plants’ ability to decompose, so leaves or plant material on the ground can cause fungal spore development if not managed properly ^[15][16][36,37]. This, along with extremely hot temperatures that can cause berry sunburn and damage the berry skin, could increase the Botrytis cinerea infection rate in grapes ^[17][38]. When the phenology of the plant and the pathogen align, more plant diseases can occur.

Depending on the magnitude of global warming, it may influence the phenology of insects by impacting the timing of their emergence and feeding patterns. Since there may be a change in the timing of grapevine phenology—for example, budbreak or foliar growth—this could lead to a change in insect survival, since insects’ timing is determined by the plant. If they are not emerging at the stages of growth needed for survival, it could cause the population to undergo food starvation or be unable to meet survival needs ^[18][39]. Elevated CO₂ concentrations can lead to the accumulation of non-structural carbohydrates in plant, which results in lower tissue nitrogen concentrations. This can lead to the need for insects to consume more foliage to meet their nitrogen needs ^[19][20][21][40,41,42]. Thus, the effects of climate change on insects are complex and involve several unknown factors, such as the introduction of new pests, competition among pests, and the presence of beneficial insects.

However, many of the highly mobile enemy insects can track climate change conditions, while this could take a while for less mobile species ^[18][39]. Vine mealybugs, for example, are less likely to leave their hideouts under the bark and on the roots to migrate towards leaves and fruit during hot conditions. However, if the daily temperatures are to increase by 2 °C or 4 °C, most regions would expect to see an increase in overall mealybug density. In California, the mealybug densities are predicted to be higher in the cooler vineyards, such as Napa and Sonoma, while being lower in warmer areas, such as the Coachella Valley ^[22][43]. The extremely hot summer temperatures in the Coachella Valley can cause mealybug mortality. In comparison, the summer temperatures in the San Joaquin Valley are not hot enough to cause high mortality rates; thus, the mealybug populations can increase significantly during the growing season. In cooler areas, such as the coastal regions, mealybug abundance follows a similar pattern to the San Joaquin Valley but with fewer summer generation cycles ^[23][44]. As many of the distributions of the pest and pathogens will be changed, interactions between them and the plants will need to be monitored. Additionally, researchers have found that pest and weed management are the main hotspots for greenhouse gas emissions in the lifecycle of grape production ^[24][25][45,46].

Grapevine yield depends on soil fertility and climatic conditions. High yields can be achieved with moderately high temperatures, sufficient light conditions, and enough nitrogen and water. Increased temperatures are beneficial for crop yield in some cool climate regions. Nemani et al. (2001) ^[8][29] found that yields and berry quality were improved in Napa and Sonoma Valleys due to lower occurrence of frost and a longer growing season. However, grapevines grown under excessive heat stress suffer photosynthesis limitation, thus contributing to significant yield reductions. Heat waves may result in a yield decrease of up to 35% in some viticultural regions ^[26][47]. Drought conditions impair grape yield, and the decrease can be variety-dependent ^[27][48]. During drought conditions, stomatal closure and the impairment of the photosynthetic machinery limit photosynthesis ^[27][48]. Increased water deficit due to reductions in precipitation in conjunction with increases in evapotranspiration influences yield. Studies have found that water deficit negatively affects yield ^[28][29][49,50]. Berry weight is one of the yield components most affected by water availability and is used for calculating the yield of a vineyard. A study showed that Shiraz vines with water deficit after flowering demonstrated significant reductions in berry weight compared to sufficiently watered vines, particularly during high-temperature seasons ^[30][51]. Another source of yield variability is temperature. A study on Sangiovese and Cabernet Sauvignon in Italy in relation to climate change reported that warmer weather resulted in higher yield variability ^[31][52].

Grape berries are composed of several hundreds of chemical compounds, including water, fermentable sugars, organic acids, nitrogen compounds, minerals, pectins, phenolic compounds, and aromatic compounds ^[32][53]. Environmental conditions, such as soil, topography, and climate, influence yields, grape composition and sensory attributes, and the quality of the wines. Higher temperatures can accelerate grape metabolism, leading to changes in the biosynthesis of basic components ^[33][54]. A report found that metabolic pathways in grapes changed once the ambient temperature was 30 °C ^[4][25]. Many studies provide evidence of grape and wine composition changes, including dramatic changes in pH, total acidity, and alcohol ^[34][35][36][5,14,55].

Elevated temperatures have been associated with sugar accumulation and organic degradation, resulting in an unbalanced sugar–acid ratio ^[37][56]. Wine made from these kinds of berries contains higher alcohol content and falls short in freshness and aromatic complexity. Warmer conditions in Slovenia led to a large reduction in total acidity in early-ripening wine varieties ^[38][39][57,58]. Grape malic acid levels are typically low in warm climate regions, since it tends to degrade at high temperatures. Lecourieux et al. found that imposing heat treatment (+8 °C, 14 days) on grape clusters at véraison and during berry ripening significantly decreased the berry concentration of malic acid, while it increased some amino acids, such as phenylalanine, γ-aminobutyric acid, proline, and leucine. The alterations in acid concentrations could have been due to the deep remodeling of transcriptomes in heated berries ^[40][59].

Anthocyanins in berries are phenolic compounds that are responsible for berry coloration. Temperature has been found to be a critical factor affecting anthocyanin synthesis due to enzymes in the metabolic pathway being temperature-sensitive ^[41][42][60,61]. If sugar accumulation starts earlier and proceeds more rapidly in the growing season under high temperatures, the berry anthocyanin concentration cannot reach the desirable levels at the harvest. This is especially true in warm-climate wine regions. Ripened berries typically have an unbalanced composition, with higher total soluble solids, low acidity, and fewer anthocyanins. Moreover, anthocyanins are highly unstable and susceptible to thermal degradation. Research has indicated that anthocyanins tend to accumulate better at 20 °C than 30 °C ^[43][62]. The anthocyanin accumulation decreases once the temperature rises above 30 °C ^[44][45][63,64]. Véraison, heat treatment, and ripening heat treatment (+8 °C, 14 days) decreased the concentrations of anthocyanins at harvest, such as delphinidin-3-O-glucoside, cyanidin-3-O-glucoside, petunidin-3-O-glucoside, peonidin-3-O-glucoside, delphinidin-3-O-(6′-acetyl) glucoside, cyanidin-3-O-(6′-acetyl) glucoside petunidin-3-O-(6′-acetyl) glucoside, and peonidin-3-O-(6′-acetyl) glucoside ^[40][59].

Increased temperatures and solar radiation will alter the secondary metabolites in berries, thus impacting flavor development ^[34][5]. The temperature range of 20–22 °C appears to be optimal for aroma formation during the grape maturation stage for most varieties ^[46][65]. Increased volatilization of aroma compounds at high temperatures has been observed. Belancic et al. reported that the terpenol content of Moscatel de Alejandria (Muscat of Alexandria) and Moscatel Rosada (Muscat Rose) was lower as a result of the vines’ overexposure to sunlight and higher berry temperature ^[47][66]. The concentrations of some aroma compounds may increase due to high temperatures, but this imparts negative effects on the wine since it breaks the balance of the aroma profile. For example, Marais et al. found that the concentrations of 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) varied with climatic regions. Warm temperatures increased the formation of TDN, which might have had a negative effect on Riesling wine, with overpowering petrol notes ^[48][67]. In a study by Lecourieux et al. (2017) ^[40][59], Cabernet Sauvignon berries exposed to high temperature showed decreased aromatic potential due to deregulation of numerous aroma and aroma precursor-related genes. The results suggested that heat treatment contributed to the decrease in volatile terpenoids caused by the repression of many key enzymes in the biosynthetic pathway. Carotenoid biosynthesis also decreased with heat treatment. High-temperature exposure also led to a drastic reduction in 2-methoxy-3-isobutylpyrazine (IBMP) content in ripe berries due to the repression of the key gene VviOMT3. VviOMT3 was reported to be responsible for the synthesis of the IBMP ^[49][68].

The impact of climate change on grapevines, berries, and wine are summarized and presented in Table 1.